Mostra a bateria num TextView

TextView batteryView = (TextView) findViewById(R.id.batteryView);

IntentFilter ifilter = new IntentFilter(Intent.ACTION_BATTERY_CHANGED);
Intent batteryStatus = getApplicationContext().registerReceiver(null, ifilter);

int level = batteryStatus.getIntExtra(BatteryManager.EXTRA_LEVEL, -1);
int scale = batteryStatus.getIntExtra(BatteryManager.EXTRA_SCALE, -1);

float batteryPct = level / (float)scale;
int batteryPercentage = (int)(batteryPct*100);

batteryView.setText("Bateria: " + batteryPercentage + "%");