diff --git a/CHANGELOG.md b/CHANGELOG.md
index 180aac0b..d4302e63 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,10 +2,11 @@
 
 # Changelog
 
-## [Unreleased]
+## [1.2.0-beta.1] - 2021-12-27
 
 ### Added
 - Status bar indicator for connected hub.
+- Basic battery OK/low indicator ([support#559]).
 
 ### Changed
 - Saving file now uses proper save dialog in Chromium browser ([support#84]).
@@ -17,6 +18,7 @@
 [support#84]: https://github.com/pybricks/support/issues/84
 [support#300]: https://github.com/pybricks/support/issues/300
 [support#369]: https://github.com/pybricks/support/issues/369
+[support#559]: https://github.com/pybricks/support/issues/559
 
 ## [1.1.0] - 2021-12-16
 
@@ -235,7 +237,8 @@ Prerelease changes are documented at [support#48].
 
 <!-- links for version headings -->
 
-[Unreleased]: https://github.com/pybricks/pybricks-code/compare/v1.1.0...HEAD
+[Unreleased]: https://github.com/pybricks/pybricks-code/compare/v1.2.0-beta.1...HEAD
+[1.2.0-beta.1]: https://github.com/pybricks/pybricks-code/compare/v1.1.0...v1.2.0-beta.1
 [1.1.0]: https://github.com/pybricks/pybricks-code/compare/v1.1.0-rc.1...v1.1.0
 [1.1.0-rc.1]: https://github.com/pybricks/pybricks-code/compare/v1.1.0-beta.6...v1.1.0-rc.1
 [1.1.0-beta.6]: https://github.com/pybricks/pybricks-code/compare/v1.1.0-beta.5...v1.1.0-beta.6
diff --git a/package.json b/package.json
index c85639f0..70a67463 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
     "name": "@pybricks/pybricks-code",
-    "version": "1.1.0",
+    "version": "1.2.0-beta.1",
     "license": "MIT",
     "author": "The Pybricks Authors",
     "repository": {
diff --git a/src/actions.ts b/src/actions.ts
index bdfb00c3..33b1a6b3 100644
--- a/src/actions.ts
+++ b/src/actions.ts
@@ -1,15 +1,16 @@
 // SPDX-License-Identifier: MIT
-// Copyright (c) 2020 The Pybricks Authors
+// Copyright (c) 2020-2021 The Pybricks Authors
 
+import { useDispatch as useReduxDispatch } from 'react-redux';
 import { Dispatch as ReduxDispatch } from 'redux';
 import { AppAction } from './app/actions';
 import { BleDIServiceAction } from './ble-device-info-service/actions';
+import { BleUartAction } from './ble-nordic-uart-service/actions';
 import {
     BlePybricksServiceAction,
     BlePybricksServiceCommandAction,
     BlePybricksServiceEventAction,
 } from './ble-pybricks-service/actions';
-import { BleUartAction } from './ble-uart/actions';
 import { BLEAction, BLEConnectAction } from './ble/actions';
 import { EditorAction } from './editor/actions';
 import { FlashFirmwareAction } from './firmware/actions';
@@ -60,3 +61,8 @@ export type Action =
  * Dispatch function.
  */
 export type Dispatch = ReduxDispatch<Action>;
+
+/**
+ * Typed version of Redux useDispatch() hook.
+ */
+export const useDispatch = (): Dispatch => useReduxDispatch<Dispatch>();
diff --git a/src/app/App.tsx b/src/app/App.tsx
index cb652143..bba931ce 100644
--- a/src/app/App.tsx
+++ b/src/app/App.tsx
@@ -2,11 +2,11 @@
 // Copyright (c) 2020-2021 The Pybricks Authors
 
 import { Classes } from '@blueprintjs/core';
-import React, { useState } from 'react';
-import { useDispatch, useSelector } from 'react-redux';
+import React, { useEffect, useState } from 'react';
 import SplitterLayout from 'react-splitter-layout';
+import { useDispatch } from '../actions';
 import Editor from '../editor/Editor';
-import { RootState } from '../reducers';
+import { useSelector } from '../reducers';
 import { toggleBoolean } from '../settings/actions';
 import { BooleanSettingId } from '../settings/defaults';
 import StatusBar from '../status-bar/StatusBar';
@@ -122,9 +122,22 @@ const Docs: React.FunctionComponent = (_props) => {
 };
 
 const App: React.FunctionComponent = (_props) => {
-    const showDocs = useSelector((s: RootState): boolean => s.settings.showDocs);
+    const darkMode = useSelector((s): boolean => s.settings.darkMode);
+    const showDocs = useSelector((s): boolean => s.settings.showDocs);
     const [isDragging, setIsDragging] = useState(false);
 
+    // darkMode class has to be applied to body element, otherwise it won't
+    // affect portals
+    useEffect(() => {
+        if (!darkMode) {
+            // no class for light mode, so nothing to do
+            return;
+        }
+
+        document.body.classList.add(Classes.DARK);
+        return () => document.body.classList.remove(Classes.DARK);
+    }, [darkMode]);
+
     return (
         <div className="pb-app h-100 w-100 p-absolute">
             <Toolbar />
diff --git a/src/ble-uart/actions.ts b/src/ble-nordic-uart-service/actions.ts
similarity index 95%
rename from src/ble-uart/actions.ts
rename to src/ble-nordic-uart-service/actions.ts
index 71e02f41..6756aa61 100644
--- a/src/ble-uart/actions.ts
+++ b/src/ble-nordic-uart-service/actions.ts
@@ -1,6 +1,7 @@
 // SPDX-License-Identifier: MIT
 // Copyright (c) 2020-2021 The Pybricks Authors
-// actions/ble-uart.ts: Actions for Bluetooth Low Energy nRF UART service
+//
+// Actions for Bluetooth Low Energy Nordic UART service
 
 import { Action } from 'redux';
 
diff --git a/src/ble-uart/protocol.ts b/src/ble-nordic-uart-service/protocol.ts
similarity index 100%
rename from src/ble-uart/protocol.ts
rename to src/ble-nordic-uart-service/protocol.ts
diff --git a/src/ble/reducers.test.ts b/src/ble/reducers.test.ts
index 8427caff..06a0662a 100644
--- a/src/ble/reducers.test.ts
+++ b/src/ble/reducers.test.ts
@@ -8,6 +8,8 @@ import {
 } from '../ble-device-info-service/actions';
 import { PnpIdVendorIdSource } from '../ble-device-info-service/protocol';
 import { HubType, LegoCompanyId } from '../ble-lwp3-service/protocol';
+import { didReceiveStatusReport } from '../ble-pybricks-service/actions';
+import { Status, statusToFlag } from '../ble-pybricks-service/protocol';
 import {
     BleDeviceDidFailToConnectReason,
     connect,
@@ -25,7 +27,9 @@ test('initial state', () => {
     expect(reducers(undefined, {} as Action)).toMatchInlineSnapshot(`
         Object {
           "connection": "ble.connection.state.disconnected",
+          "deviceBatteryCharging": false,
           "deviceFirmwareVersion": "",
+          "deviceLowBatteryWarning": false,
           "deviceName": "",
           "deviceType": "",
         }
@@ -113,3 +117,31 @@ test('deviceFirmwareVersion', () => {
             .deviceFirmwareVersion,
     ).toBe('');
 });
+
+test('deviceLowBatteryWarning', () => {
+    expect(
+        reducers(
+            { deviceLowBatteryWarning: false } as State,
+            didReceiveStatusReport(statusToFlag(Status.BatteryLowVoltageWarning)),
+        ).deviceLowBatteryWarning,
+    ).toBeTruthy();
+
+    expect(
+        reducers(
+            { deviceLowBatteryWarning: true } as State,
+            didReceiveStatusReport(~statusToFlag(Status.BatteryLowVoltageWarning)),
+        ).deviceLowBatteryWarning,
+    ).toBeFalsy();
+
+    expect(
+        reducers({ deviceLowBatteryWarning: true } as State, didDisconnect())
+            .deviceLowBatteryWarning,
+    ).toBeFalsy();
+});
+
+test('deviceBatteryCharging', () => {
+    expect(
+        reducers({ deviceBatteryCharging: true } as State, didDisconnect())
+            .deviceBatteryCharging,
+    ).toBeFalsy();
+});
diff --git a/src/ble/reducers.ts b/src/ble/reducers.ts
index 449fe567..c14e089b 100644
--- a/src/ble/reducers.ts
+++ b/src/ble/reducers.ts
@@ -8,6 +8,8 @@ import { Reducer, combineReducers } from 'redux';
 import { Action } from '../actions';
 import { BleDIServiceActionType } from '../ble-device-info-service/actions';
 import { getHubTypeName } from '../ble-device-info-service/protocol';
+import { BlePybricksServiceEventActionType } from '../ble-pybricks-service/actions';
+import { Status, statusToFlag } from '../ble-pybricks-service/protocol';
 import { BleDeviceActionType } from './actions';
 
 /**
@@ -85,9 +87,34 @@ const deviceFirmwareVersion: Reducer<string, Action> = (state = '', action) => {
     }
 };
 
+const deviceLowBatteryWarning: Reducer<boolean, Action> = (state = false, action) => {
+    switch (action.type) {
+        case BleDeviceActionType.DidDisconnect:
+            return false;
+        case BlePybricksServiceEventActionType.DidReceiveStatusReport:
+            return Boolean(
+                action.statusFlags & statusToFlag(Status.BatteryLowVoltageWarning),
+            );
+        default:
+            return state;
+    }
+};
+
+const deviceBatteryCharging: Reducer<boolean, Action> = (state = false, action) => {
+    switch (action.type) {
+        case BleDeviceActionType.DidDisconnect:
+            return false;
+        // TODO: hub does not currently have a status flag for this
+        default:
+            return state;
+    }
+};
+
 export default combineReducers({
     connection,
     deviceName,
     deviceType,
     deviceFirmwareVersion,
+    deviceLowBatteryWarning,
+    deviceBatteryCharging,
 });
diff --git a/src/ble-uart/sagas.ts b/src/ble/sagas.ts
similarity index 99%
rename from src/ble-uart/sagas.ts
rename to src/ble/sagas.ts
index e8ff3741..d591a798 100644
--- a/src/ble-uart/sagas.ts
+++ b/src/ble/sagas.ts
@@ -27,6 +27,18 @@ import {
     pnpIdUUID,
     softwareRevisionStringUUID,
 } from '../ble-device-info-service/protocol';
+import {
+    BleUartActionType,
+    BleUartWriteAction,
+    didFailToWrite as didFailToWriteUart,
+    didNotify as didNotifyUart,
+    didWrite as didWriteUart,
+} from '../ble-nordic-uart-service/actions';
+import {
+    RxCharUUID as uartRxCharUUID,
+    ServiceUUID as uartServiceUUID,
+    TxCharUUID as uartTxCharUUID,
+} from '../ble-nordic-uart-service/protocol';
 import {
     BlePybricksServiceActionType,
     didFailToWriteCommand,
@@ -37,6 +49,8 @@ import {
     ControlCharacteristicUUID as pybricksCommandCharacteristicUUID,
     ServiceUUID as pybricksServiceUUID,
 } from '../ble-pybricks-service/protocol';
+import { RootState } from '../reducers';
+import { ensureError } from '../utils';
 import {
     BLEActionType,
     BleDeviceActionType as BLEDeviceActionType,
@@ -49,22 +63,8 @@ import {
     didDisconnect,
     didFailToConnect,
     disconnect as disconnectAction,
-} from '../ble/actions';
-import { BleConnectionState } from '../ble/reducers';
-import { RootState } from '../reducers';
-import { ensureError } from '../utils';
-import {
-    BleUartActionType,
-    BleUartWriteAction,
-    didFailToWrite as didFailToWriteUart,
-    didNotify as didNotifyUart,
-    didWrite as didWriteUart,
 } from './actions';
-import {
-    RxCharUUID as uartRxCharUUID,
-    ServiceUUID as uartServiceUUID,
-    TxCharUUID as uartTxCharUUID,
-} from './protocol';
+import { BleConnectionState } from './reducers';
 
 const decoder = new TextDecoder();
 
diff --git a/src/editor/Editor.tsx b/src/editor/Editor.tsx
index 435130a9..99f777cf 100644
--- a/src/editor/Editor.tsx
+++ b/src/editor/Editor.tsx
@@ -12,10 +12,10 @@ import tomorrowNightEightiesTheme from 'monaco-themes/themes/Tomorrow-Night-Eigh
 import xcodeTheme from 'monaco-themes/themes/Xcode_default.json';
 import React, { useEffect, useRef } from 'react';
 import MonacoEditor, { monaco } from 'react-monaco-editor';
-import { useDispatch, useSelector } from 'react-redux';
 import { IDisposable } from 'xterm';
+import { useDispatch } from '../actions';
 import { compile } from '../mpy/actions';
-import { RootState } from '../reducers';
+import { useSelector } from '../reducers';
 import { toggleBoolean } from '../settings/actions';
 import { BooleanSettingId } from '../settings/defaults';
 import { isMacOS } from '../utils/os';
@@ -63,7 +63,7 @@ const xcodeId = 'xcode';
 monaco.editor.defineTheme(xcodeId, xcodeTheme as monaco.editor.IStandaloneThemeData);
 
 const contextMenu = (_props: ContextMenu2ContentProps): JSX.Element => {
-    const editor = useSelector((state: RootState) => state.editor.current);
+    const editor = useSelector((s) => s.editor.current);
 
     const [i18n] = useI18n({ id: 'editor', translations: { en }, fallback: en });
 
@@ -143,7 +143,7 @@ const Editor: React.FunctionComponent = (_props) => {
         return () => window.removeEventListener('storage', onStorage);
     });
 
-    const darkMode = useSelector((state: RootState) => state.settings.darkMode);
+    const darkMode = useSelector((s) => s.settings.darkMode);
 
     const [i18n] = useI18n({ id: 'editor', translations: { en }, fallback: en });
 
diff --git a/src/editor/OpenButton.tsx b/src/editor/OpenButton.tsx
index 0728701b..b5e77ded 100644
--- a/src/editor/OpenButton.tsx
+++ b/src/editor/OpenButton.tsx
@@ -2,9 +2,9 @@
 // Copyright (c) 2020-2021 The Pybricks Authors
 
 import React from 'react';
-import { useDispatch, useSelector } from 'react-redux';
+import { useDispatch } from '../actions';
 import * as notificationActions from '../notifications/actions';
-import { RootState } from '../reducers';
+import { useSelector } from '../reducers';
 import OpenFileButton, { OpenFileButtonProps } from '../toolbar/OpenFileButton';
 import { TooltipId } from '../toolbar/i18n';
 import * as editorActions from './actions';
@@ -13,7 +13,7 @@ import openIcon from './open.svg';
 type OpenButtonProps = Pick<OpenFileButtonProps, 'id'>;
 
 const OpenButton: React.FunctionComponent<OpenButtonProps> = (props) => {
-    const editor = useSelector((state: RootState) => state.editor.current);
+    const editor = useSelector((s) => s.editor.current);
     const dispatch = useDispatch();
 
     return (
diff --git a/src/editor/SaveAsButton.tsx b/src/editor/SaveAsButton.tsx
index a676a2f3..26e991d9 100644
--- a/src/editor/SaveAsButton.tsx
+++ b/src/editor/SaveAsButton.tsx
@@ -2,9 +2,9 @@
 // Copyright (c) 2020-2021 The Pybricks Authors
 
 import React from 'react';
-import { useDispatch, useSelector } from 'react-redux';
+import { useDispatch } from '../actions';
 import * as editorActions from '../editor/actions';
-import { RootState } from '../reducers';
+import { useSelector } from '../reducers';
 import ActionButton, { ActionButtonProps } from '../toolbar/ActionButton';
 import { TooltipId } from '../toolbar/i18n';
 import downloadIcon from './save.svg';
@@ -13,7 +13,7 @@ type SaveAsButtonProps = Pick<ActionButtonProps, 'id'> &
     Pick<ActionButtonProps, 'keyboardShortcut'>;
 
 const SaveAsButton: React.FunctionComponent<SaveAsButtonProps> = (props) => {
-    const editor = useSelector((state: RootState) => state.editor.current);
+    const editor = useSelector((s) => s.editor.current);
 
     const dispatch = useDispatch();
 
diff --git a/src/error-log/sagas.test.ts b/src/error-log/sagas.test.ts
index d980bb03..664e0991 100644
--- a/src/error-log/sagas.test.ts
+++ b/src/error-log/sagas.test.ts
@@ -2,8 +2,8 @@
 // Copyright (c) 2020 The Pybricks Authors
 
 import { AsyncSaga } from '../../test';
+import { didFailToWrite } from '../ble-nordic-uart-service/actions';
 import { eventProtocolError } from '../ble-pybricks-service/actions';
-import { didFailToWrite } from '../ble-uart/actions';
 import {
     BleDeviceFailToConnectReasonType,
     didFailToConnect as bleDidFailToConnect,
diff --git a/src/error-log/sagas.ts b/src/error-log/sagas.ts
index c4e40ea3..b918f7db 100644
--- a/src/error-log/sagas.ts
+++ b/src/error-log/sagas.ts
@@ -2,11 +2,14 @@
 // Copyright (c) 2020-2021 The Pybricks Authors
 
 import { takeEvery } from 'typed-redux-saga/macro';
+import {
+    BleUartActionType,
+    BleUartDidFailToWriteAction,
+} from '../ble-nordic-uart-service/actions';
 import {
     BlePybricksServiceEventActionType,
     BlePybricksServiceEventProtocolErrorAction,
 } from '../ble-pybricks-service/actions';
-import { BleUartActionType, BleUartDidFailToWriteAction } from '../ble-uart/actions';
 import {
     BleDeviceActionType,
     BleDeviceDidFailToConnectAction,
diff --git a/src/firmware/FlashButton.tsx b/src/firmware/FlashButton.tsx
index 996a1fa9..781f14b2 100644
--- a/src/firmware/FlashButton.tsx
+++ b/src/firmware/FlashButton.tsx
@@ -2,11 +2,11 @@
 // Copyright (c) 2020-2021 The Pybricks Authors
 
 import React from 'react';
-import { useDispatch, useSelector } from 'react-redux';
+import { useDispatch } from '../actions';
 import { BleConnectionState } from '../ble/reducers';
 import { BootloaderConnectionState } from '../lwp3-bootloader/reducers';
 import * as notificationActions from '../notifications/actions';
-import { RootState } from '../reducers';
+import { useSelector } from '../reducers';
 import OpenFileButton, { OpenFileButtonProps } from '../toolbar/OpenFileButton';
 import { TooltipId } from '../toolbar/i18n';
 import { flashFirmware } from './actions';
@@ -15,12 +15,10 @@ import firmwareIcon from './firmware.svg';
 type FlashButtonProps = Pick<OpenFileButtonProps, 'id'>;
 
 const FlashButton: React.FunctionComponent<FlashButtonProps> = (props) => {
-    const bootloaderConnection = useSelector(
-        (state: RootState) => state.bootloader.connection,
-    );
-    const bleConnection = useSelector((state: RootState) => state.ble.connection);
-    const flashing = useSelector((state: RootState) => state.firmware.flashing);
-    const progress = useSelector((state: RootState) => state.firmware.progress);
+    const bootloaderConnection = useSelector((s) => s.bootloader.connection);
+    const bleConnection = useSelector((s) => s.ble.connection);
+    const flashing = useSelector((s) => s.firmware.flashing);
+    const progress = useSelector((s) => s.firmware.progress);
 
     const dispatch = useDispatch();
 
diff --git a/src/hub/BluetoothButton.tsx b/src/hub/BluetoothButton.tsx
index 3e91b38b..51595388 100644
--- a/src/hub/BluetoothButton.tsx
+++ b/src/hub/BluetoothButton.tsx
@@ -2,11 +2,11 @@
 // Copyright (c) 2020-2021 The Pybricks Authors
 
 import React from 'react';
-import { useDispatch, useSelector } from 'react-redux';
+import { useDispatch } from '../actions';
 import { toggleBluetooth } from '../ble/actions';
 import { BleConnectionState } from '../ble/reducers';
 import { BootloaderConnectionState } from '../lwp3-bootloader/reducers';
-import { RootState } from '../reducers';
+import { useSelector } from '../reducers';
 import ActionButton, { ActionButtonProps } from '../toolbar/ActionButton';
 import { TooltipId } from '../toolbar/i18n';
 import btConnectedIcon from './bt-connected.svg';
@@ -15,10 +15,8 @@ import btDisconnectedIcon from './bt-disconnected.svg';
 type BluetoothButtonProps = Pick<ActionButtonProps, 'id'>;
 
 const BluetoothButton: React.FunctionComponent<BluetoothButtonProps> = (props) => {
-    const bootloaderConnection = useSelector(
-        (state: RootState) => state.bootloader.connection,
-    );
-    const bleConnection = useSelector((state: RootState) => state.ble.connection);
+    const bootloaderConnection = useSelector((s) => s.bootloader.connection);
+    const bleConnection = useSelector((s) => s.ble.connection);
 
     const isDisconnected =
         bootloaderConnection === BootloaderConnectionState.Disconnected &&
diff --git a/src/hub/RunButton.tsx b/src/hub/RunButton.tsx
index 409e4719..31961d62 100644
--- a/src/hub/RunButton.tsx
+++ b/src/hub/RunButton.tsx
@@ -2,8 +2,8 @@
 // Copyright (c) 2020-2021 The Pybricks Authors
 
 import React from 'react';
-import { useDispatch, useSelector } from 'react-redux';
-import { RootState } from '../reducers';
+import { useDispatch } from '../actions';
+import { useSelector } from '../reducers';
 import ActionButton, { ActionButtonProps } from '../toolbar/ActionButton';
 import { TooltipId } from '../toolbar/i18n';
 import { downloadAndRun } from './actions';
@@ -14,11 +14,9 @@ type RunButtonProps = Pick<ActionButtonProps, 'id'> &
     Pick<ActionButtonProps, 'keyboardShortcut'>;
 
 const RunButton: React.FunctionComponent<RunButtonProps> = (props) => {
-    const editor = useSelector((state: RootState) => state.editor.current);
-    const downloadProgress = useSelector(
-        (state: RootState) => state.hub.downloadProgress,
-    );
-    const runtime = useSelector((state: RootState) => state.hub.runtime);
+    const editor = useSelector((s) => s.editor.current);
+    const downloadProgress = useSelector((s) => s.hub.downloadProgress);
+    const runtime = useSelector((s) => s.hub.runtime);
 
     const dispatch = useDispatch();
 
diff --git a/src/hub/StopButton.tsx b/src/hub/StopButton.tsx
index c433c0e2..76fb80b1 100644
--- a/src/hub/StopButton.tsx
+++ b/src/hub/StopButton.tsx
@@ -2,8 +2,8 @@
 // Copyright (c) 2020-2021 The Pybricks Authors
 
 import React from 'react';
-import { useDispatch, useSelector } from 'react-redux';
-import { RootState } from '../reducers';
+import { useDispatch } from '../actions';
+import { useSelector } from '../reducers';
 import ActionButton, { ActionButtonProps } from '../toolbar/ActionButton';
 import { TooltipId } from '../toolbar/i18n';
 import { stop } from './actions';
@@ -14,7 +14,7 @@ type StopButtonProps = Pick<ActionButtonProps, 'id'> &
     Pick<ActionButtonProps, 'keyboardShortcut'>;
 
 const StopButton: React.FunctionComponent<StopButtonProps> = (props) => {
-    const runtime = useSelector((state: RootState) => state.hub.runtime);
+    const runtime = useSelector((s) => s.hub.runtime);
 
     const dispatch = useDispatch();
 
diff --git a/src/hub/sagas.test.ts b/src/hub/sagas.test.ts
index 0528b4f2..1e2b5ff9 100644
--- a/src/hub/sagas.test.ts
+++ b/src/hub/sagas.test.ts
@@ -4,12 +4,16 @@
 import { mock } from 'jest-mock-extended';
 import { monaco } from 'react-monaco-editor';
 import { AsyncSaga } from '../../test';
+import {
+    BleUartActionType,
+    BleUartWriteAction,
+    didWrite,
+} from '../ble-nordic-uart-service/actions';
 import {
     BlePybricksServiceCommandActionType,
     BlePybricksServiceCommandSendStopUserProgram,
     didSendCommand,
 } from '../ble-pybricks-service/actions';
-import { BleUartActionType, BleUartWriteAction, didWrite } from '../ble-uart/actions';
 import { MpyActionType, didCompile } from '../mpy/actions';
 import { createCountFunc } from '../utils/iter';
 import {
diff --git a/src/hub/sagas.ts b/src/hub/sagas.ts
index f1fdae24..ac855a52 100644
--- a/src/hub/sagas.ts
+++ b/src/hub/sagas.ts
@@ -13,19 +13,19 @@ import {
     takeEvery,
 } from 'typed-redux-saga/macro';
 import { Action } from '../actions';
+import {
+    BleUartActionType,
+    BleUartDidFailToWriteAction,
+    BleUartDidWriteAction,
+    write,
+} from '../ble-nordic-uart-service/actions';
+import { SafeTxCharLength } from '../ble-nordic-uart-service/protocol';
 import {
     BlePybricksServiceCommandActionType,
     BlePybricksServiceCommandDidFailToSendAction,
     BlePybricksServiceCommandDidSendAction,
     sendStopUserProgramCommand,
 } from '../ble-pybricks-service/actions';
-import {
-    BleUartActionType,
-    BleUartDidFailToWriteAction,
-    BleUartDidWriteAction,
-    write,
-} from '../ble-uart/actions';
-import { SafeTxCharLength } from '../ble-uart/protocol';
 import { BleDeviceActionType } from '../ble/actions';
 import {
     MpyActionType,
diff --git a/src/index.tsx b/src/index.tsx
index 778710fc..18da4b63 100644
--- a/src/index.tsx
+++ b/src/index.tsx
@@ -1,7 +1,6 @@
 // SPDX-License-Identifier: MIT
 // Copyright (c) 2020-2021 The Pybricks Authors
 
-import { Classes } from '@blueprintjs/core';
 import { I18nContext } from '@shopify/react-i18n';
 import React from 'react';
 import ReactDOM from 'react-dom';
@@ -41,30 +40,6 @@ const store = createStore(
     applyMiddleware(sagaMiddleware, loggerMiddleware),
 );
 
-// Hook in blueprints dark mode class to setting
-let oldDarkMode = false;
-store.subscribe(() => {
-    const newDarkMode = store.getState().settings.darkMode;
-    if (newDarkMode !== oldDarkMode) {
-        if (newDarkMode) {
-            document.body.classList.add(Classes.DARK);
-            for (const frame of document.getElementsByTagName('iframe')) {
-                frame.contentWindow?.document.documentElement.classList.add(
-                    Classes.DARK,
-                );
-            }
-        } else {
-            document.body.classList.remove(Classes.DARK);
-            for (const frame of document.getElementsByTagName('iframe')) {
-                frame.contentWindow?.document.documentElement.classList.remove(
-                    Classes.DARK,
-                );
-            }
-        }
-        oldDarkMode = newDarkMode;
-    }
-});
-
 // special styling for beta versions
 if (appVersion.match(/beta/)) {
     document.body.classList.add('pb-beta');
diff --git a/src/licenses/LicenseDialog.tsx b/src/licenses/LicenseDialog.tsx
index d99356b8..bb20d3f3 100644
--- a/src/licenses/LicenseDialog.tsx
+++ b/src/licenses/LicenseDialog.tsx
@@ -14,9 +14,9 @@ import {
 } from '@blueprintjs/core';
 import { useI18n } from '@shopify/react-i18n';
 import React from 'react';
-import { useDispatch, useSelector } from 'react-redux';
+import { useDispatch } from '../actions';
 import { appName } from '../app/constants';
-import { RootState } from '../reducers';
+import { useSelector } from '../reducers';
 import { fetchList, select } from './actions';
 import { LicenseStringId } from './i18n';
 import en from './i18n.en.json';
@@ -31,7 +31,7 @@ type LicenseListPanelProps = {
 const LicenseListPanel: React.VoidFunctionComponent<LicenseListPanelProps> = (
     props,
 ) => {
-    const licenseList = useSelector((state: RootState) => state.licenses.list);
+    const licenseList = useSelector((s) => s.licenses.list);
 
     return (
         <div className="pb-license-list">
@@ -54,7 +54,7 @@ const LicenseListPanel: React.VoidFunctionComponent<LicenseListPanelProps> = (
 };
 
 const LicenseInfoPanel = React.forwardRef<HTMLDivElement>((_props, ref) => {
-    const licenseInfo = useSelector((state: RootState) => state.licenses.selected);
+    const licenseInfo = useSelector((s) => s.licenses.selected);
 
     const [i18n] = useI18n({ id: 'license', translations: { en }, fallback: en });
 
diff --git a/src/reducers.ts b/src/reducers.ts
index 04c5f38d..d01683df 100644
--- a/src/reducers.ts
+++ b/src/reducers.ts
@@ -1,6 +1,7 @@
 // SPDX-License-Identifier: MIT
 // Copyright (c) 2020-2021 The Pybricks Authors
 
+import { TypedUseSelectorHook, useSelector as useReduxSelector } from 'react-redux';
 import { Reducer, combineReducers } from 'redux';
 import app from './app/reducers';
 import ble from './ble/reducers';
@@ -31,3 +32,8 @@ export const rootReducer = combineReducers({
 type StateFromReducer<R> = R extends Reducer<infer S> ? S : never;
 
 export type RootState = StateFromReducer<typeof rootReducer>;
+
+/**
+ * Typed version of react-redux useSelector() hook.
+ */
+export const useSelector: TypedUseSelectorHook<RootState> = useReduxSelector;
diff --git a/src/sagas.ts b/src/sagas.ts
index 2ccf8d5b..412c14d6 100644
--- a/src/sagas.ts
+++ b/src/sagas.ts
@@ -5,7 +5,7 @@ import { all, put } from 'typed-redux-saga/macro';
 import { didStart } from './app/actions';
 import app from './app/sagas';
 import blePybricksService from './ble-pybricks-service/sagas';
-import bleUart from './ble-uart/sagas';
+import ble from './ble/sagas';
 import editor from './editor/sagas';
 import errorLog from './error-log/sagas';
 import flashFirmware from './firmware/sagas';
@@ -23,7 +23,7 @@ export default function* (): Generator {
     yield* all([
         app(),
         blePybricksService(),
-        bleUart(),
+        ble(),
         lwp3BootloaderBle(),
         lwp3BootloaderProtocol(),
         editor(),
diff --git a/src/settings/SettingsDrawer.tsx b/src/settings/SettingsDrawer.tsx
index 85221b76..7dd6686f 100644
--- a/src/settings/SettingsDrawer.tsx
+++ b/src/settings/SettingsDrawer.tsx
@@ -19,8 +19,8 @@ import {
 import { Tooltip2 } from '@blueprintjs/popover2';
 import { useI18n } from '@shopify/react-i18n';
 import React, { useMemo, useState } from 'react';
-import { useDispatch, useSelector } from 'react-redux';
 import AboutDialog from '../about/AboutDialog';
+import { useDispatch } from '../actions';
 import { checkForUpdate, installPrompt, reload } from '../app/actions';
 import {
     pybricksBugReportsUrl,
@@ -30,7 +30,7 @@ import {
     tooltipDelay,
 } from '../app/constants';
 import { pseudolocalize } from '../i18n';
-import { RootState } from '../reducers';
+import { useSelector } from '../reducers';
 import ExternalLinkIcon from '../utils/ExternalLinkIcon';
 import { isMacOS } from '../utils/os';
 import { setBoolean, setString, toggleBoolean } from './actions';
@@ -47,31 +47,17 @@ type SettingsProps = {
 const SettingsDrawer: React.FunctionComponent<SettingsProps> = (props) => {
     const [isAboutDialogOpen, setIsAboutDialogOpen] = useState(false);
 
-    const showDocs = useSelector((state: RootState) => state.settings.showDocs);
-    const darkMode = useSelector((state: RootState) => state.settings.darkMode);
-    const flashCurrentProgram = useSelector(
-        (state: RootState) => state.settings.flashCurrentProgram,
-    );
-    const serviceWorker = useSelector((state: RootState) => state.app.serviceWorker);
-    const checkingForUpdate = useSelector(
-        (state: RootState) => state.app.checkingForUpdate,
-    );
-    const updateAvailable = useSelector(
-        (state: RootState) => state.app.updateAvailable,
-    );
-    const beforeInstallPrompt = useSelector(
-        (state: RootState) => state.app.beforeInstallPrompt,
-    );
-    const promptingInstall = useSelector(
-        (state: RootState) => state.app.promptingInstall,
-    );
-    const readyForOfflineUse = useSelector(
-        (state: RootState) => state.app.readyForOfflineUse,
-    );
-    const hubName = useSelector((state: RootState) => state.settings.hubName);
-    const isHubNameValid = useSelector(
-        (state: RootState) => state.settings.isHubNameValid,
-    );
+    const showDocs = useSelector((s) => s.settings.showDocs);
+    const darkMode = useSelector((s) => s.settings.darkMode);
+    const flashCurrentProgram = useSelector((s) => s.settings.flashCurrentProgram);
+    const serviceWorker = useSelector((s) => s.app.serviceWorker);
+    const checkingForUpdate = useSelector((s) => s.app.checkingForUpdate);
+    const updateAvailable = useSelector((s) => s.app.updateAvailable);
+    const beforeInstallPrompt = useSelector((s) => s.app.beforeInstallPrompt);
+    const promptingInstall = useSelector((s) => s.app.promptingInstall);
+    const readyForOfflineUse = useSelector((s) => s.app.readyForOfflineUse);
+    const hubName = useSelector((s) => s.settings.hubName);
+    const isHubNameValid = useSelector((s) => s.settings.isHubNameValid);
 
     const dispatch = useDispatch();
 
diff --git a/src/status-bar/StatusBar.tsx b/src/status-bar/StatusBar.tsx
index 08a4830a..6f96493d 100644
--- a/src/status-bar/StatusBar.tsx
+++ b/src/status-bar/StatusBar.tsx
@@ -1,32 +1,32 @@
 // SPDX-License-Identifier: MIT
 // Copyright (c) 2020-2021 The Pybricks Authors
 
-import { Button } from '@blueprintjs/core';
-import { Classes as Classes2, Popover2 } from '@blueprintjs/popover2';
+import { Button, Intent, ProgressBar } from '@blueprintjs/core';
+import { Classes as Classes2, Popover2, Popover2Props } from '@blueprintjs/popover2';
 import { useI18n } from '@shopify/react-i18n';
 import React from 'react';
-import { useSelector } from 'react-redux';
 import { BleConnectionState } from '../ble/reducers';
-import { RootState } from '../reducers';
+import { useSelector } from '../reducers';
 import { MessageId } from './i18n';
 import en from './i18n.en.json';
 
 import './status-bar.scss';
 
+const commonPopoverProps: Partial<Popover2Props> = {
+    popoverClassName: Classes2.POPOVER2_CONTENT_SIZING,
+    placement: 'top',
+};
+
 const HubInfoButton: React.VFC = (_props) => {
-    const deviceName = useSelector((state: RootState) => state.ble.deviceName);
-    const deviceType = useSelector((state: RootState) => state.ble.deviceType);
-    const deviceFirmwareVersion = useSelector(
-        (state: RootState) => state.ble.deviceFirmwareVersion,
-    );
+    const deviceName = useSelector((s) => s.ble.deviceName);
+    const deviceType = useSelector((s) => s.ble.deviceType);
+    const deviceFirmwareVersion = useSelector((s) => s.ble.deviceFirmwareVersion);
 
     const [i18n] = useI18n({ id: 'statusBar', translations: { en }, fallback: en });
 
     return (
         <Popover2
-            popoverClassName={Classes2.POPOVER2_CONTENT_SIZING}
-            rootBoundary="document"
-            placement="top"
+            {...commonPopoverProps}
             content={
                 <table className="no-wrap">
                     <tbody>
@@ -65,8 +65,39 @@ const HubInfoButton: React.VFC = (_props) => {
     );
 };
 
+const BatteryIndicator: React.VFC = (_props) => {
+    const charging = useSelector((s) => s.ble.deviceBatteryCharging);
+    const lowBatteryWarning = useSelector((s) => s.ble.deviceLowBatteryWarning);
+
+    const [i18n] = useI18n({ id: 'statusBar', translations: { en }, fallback: en });
+
+    return (
+        <Popover2
+            {...commonPopoverProps}
+            content={
+                <span className="no-wrap">
+                    {i18n.translate(
+                        lowBatteryWarning ? MessageId.BatteryLow : MessageId.BatteryOk,
+                    )}
+                </span>
+            }
+        >
+            <div className="pb-battery-indicator" style={{ cursor: 'pointer' }}>
+                <div className="pb-battery-indicator-body">
+                    <ProgressBar
+                        animate={charging}
+                        stripes={charging}
+                        intent={lowBatteryWarning ? Intent.DANGER : Intent.SUCCESS}
+                    />
+                </div>
+                <div className="pb-battery-indicator-tip" />
+            </div>
+        </Popover2>
+    );
+};
+
 const StatusBar: React.VFC = (_props) => {
-    const connection = useSelector((state: RootState) => state.ble.connection);
+    const connection = useSelector((s) => s.ble.connection);
 
     return (
         <div
@@ -75,7 +106,12 @@ const StatusBar: React.VFC = (_props) => {
             aria-live="off"
             onContextMenu={(e): void => e.preventDefault()}
         >
-            {connection === BleConnectionState.Connected && <HubInfoButton />}
+            {connection === BleConnectionState.Connected && (
+                <>
+                    <HubInfoButton />
+                    <BatteryIndicator />
+                </>
+            )}
         </div>
     );
 };
diff --git a/src/status-bar/i18n.en.json b/src/status-bar/i18n.en.json
index 1222b2ff..61d9161a 100644
--- a/src/status-bar/i18n.en.json
+++ b/src/status-bar/i18n.en.json
@@ -3,5 +3,9 @@
         "connectedTo": "Connected to:",
         "hubType": "Hub type:",
         "firmware": "Firmware:"
+    },
+    "battery": {
+        "low": "Battery is low. Hub will turn off soon.",
+        "ok": "Battery level is OK."
     }
 }
diff --git a/src/status-bar/i18n.ts b/src/status-bar/i18n.ts
index 5e128865..48076c76 100644
--- a/src/status-bar/i18n.ts
+++ b/src/status-bar/i18n.ts
@@ -4,6 +4,8 @@
 // Status bar translation keys.
 
 export enum MessageId {
+    BatteryLow = 'battery.low',
+    BatteryOk = 'battery.ok',
     HubInfoConnectedTo = 'hubInfo.connectedTo',
     HubInfoHubType = 'hubInfo.hubType',
     HubInfoFirmware = 'hubInfo.firmware',
diff --git a/src/status-bar/status-bar.scss b/src/status-bar/status-bar.scss
index 52be658d..e823749a 100644
--- a/src/status-bar/status-bar.scss
+++ b/src/status-bar/status-bar.scss
@@ -11,6 +11,7 @@
     background-color: $pb-pybricks-blue;
     height: $pb-status-bar-height;
     width: 100vw;
+    padding-inline: 5px;
     display: flex;
     align-items: center;
 }
@@ -19,3 +20,41 @@
 .pb-status-bar :first-child {
     margin-left: auto;
 }
+
+.pb-battery-indicator {
+    display: flex;
+    flex-direction: row;
+    align-items: center;
+    margin: 5px;
+}
+
+.pb-battery-indicator-body {
+    border-radius: 3px;
+    border: 2px solid $pt-text-color;
+    background-color: $pt-text-color;
+    width: 30px;
+}
+
+.pb-battery-indicator-body .#{$ns}-progress-bar {
+    height: 12px;
+}
+
+.pb-battery-indicator-body .#{$ns}-progress-bar,
+.pb-battery-indicator-body .#{$ns}-progress-meter {
+    border-radius: 3px;
+}
+
+.pb-battery-indicator-tip {
+    border-top-right-radius: 1px;
+    border-bottom-right-radius: 1px;
+    border: 1px solid $pt-text-color;
+    background-color: $pt-text-color;
+    width: 3px;
+    height: 8px;
+}
+
+.#{$ns}-dark .pb-battery-indicator-body,
+.#{$ns}-dark .pb-battery-indicator-tip {
+    border-color: $pt-dark-text-color;
+    background-color: $pt-dark-text-color;
+}
diff --git a/src/terminal/Terminal.tsx b/src/terminal/Terminal.tsx
index 0e2aae53..7dcf7b3b 100644
--- a/src/terminal/Terminal.tsx
+++ b/src/terminal/Terminal.tsx
@@ -5,10 +5,10 @@ import { Menu, MenuDivider, MenuItem, ResizeSensor } from '@blueprintjs/core';
 import { ContextMenu2, ContextMenu2ContentProps } from '@blueprintjs/popover2';
 import { useI18n } from '@shopify/react-i18n';
 import React, { useContext, useEffect, useMemo, useRef } from 'react';
-import { useDispatch, useSelector } from 'react-redux';
 import { Terminal as XTerm } from 'xterm';
 import { FitAddon } from 'xterm-addon-fit';
-import { RootState } from '../reducers';
+import { useDispatch } from '../actions';
+import { useSelector } from '../reducers';
 import { isMacOS } from '../utils/os';
 import { TerminalContext } from './TerminalContext';
 import { receiveData } from './actions';
@@ -100,7 +100,7 @@ function createContextMenu(
 const Terminal: React.FC = (_props) => {
     const { xterm, fitAddon } = useMemo(createXTerm, [createXTerm]);
     const terminalRef = useRef<HTMLDivElement>(null);
-    const darkMode = useSelector((state: RootState) => state.settings.darkMode);
+    const darkMode = useSelector((s) => s.settings.darkMode);
     const dispatch = useDispatch();
     const terminalStream = useContext(TerminalContext);
 
diff --git a/src/terminal/sagas.test.ts b/src/terminal/sagas.test.ts
index 9ef0953c..495eea54 100644
--- a/src/terminal/sagas.test.ts
+++ b/src/terminal/sagas.test.ts
@@ -9,7 +9,7 @@ import {
     didFailToWrite,
     didNotify,
     didWrite,
-} from '../ble-uart/actions';
+} from '../ble-nordic-uart-service/actions';
 import { HubChecksumMessageAction, HubMessageActionType } from '../hub/actions';
 import { HubRuntimeState } from '../hub/reducers';
 import { createCountFunc } from '../utils/iter';
diff --git a/src/terminal/sagas.ts b/src/terminal/sagas.ts
index c3722ffc..bd5f021f 100644
--- a/src/terminal/sagas.ts
+++ b/src/terminal/sagas.ts
@@ -13,8 +13,12 @@ import {
     takeEvery,
 } from 'typed-redux-saga/macro';
 import { Action } from '../actions';
-import { BleUartActionType, BleUartDidNotifyAction, write } from '../ble-uart/actions';
-import { SafeTxCharLength } from '../ble-uart/protocol';
+import {
+    BleUartActionType,
+    BleUartDidNotifyAction,
+    write,
+} from '../ble-nordic-uart-service/actions';
+import { SafeTxCharLength } from '../ble-nordic-uart-service/protocol';
 import { checksum } from '../hub/actions';
 import { HubRuntimeState } from '../hub/reducers';
 import { RootState } from '../reducers';