On several Android forums around the web, Android users have been regularly reporting rapidly draining batteries after flashing custom ROMs (such as Cyanogenmod 7) to their devices. In what follows, we will provide you with a step-by-step solution to said problem.
The battery indicator in the status/notification bar is a reflection of the batterystats.bin file in thedata/system/ directory. Every time a custom ROM is flashed on to a device, it is recommended that the battery be software recalibrated or user might experienced an accelerated battery drain.
The accelerated drain is caused by the “off-mark” battery stats file that fools the battery into “thinking” that it has reached the end or peak of its capacity before it is actually fully drained or charged. To remedy said problem,
- Charge your device to 100%. If after a previous attempt to calibrate the battery, your device fails to charge above a fixed level, it is possible that it has been calibrated incorrectly. If so, power it off and plug it in for charging until the LED indicator turns green. If your device does not sport an LED indicator, it probably shows an on-screen graphic. If not, you’ll have to check the battery level by powering it on.
- Reboot into recovery. If your custom ROM does not provide a shortcut to rebooting into recovery, you may use ROM Manager to do so or simply power off your device for a more manual approach. If your device is already powered off, hold down the (device-specific) key combination that brings up the bootloader and select Recovery.
- Wipe Battery Stats. The following screenshots demonstrate how to wipe battery stats in ClockworkMod Recovery v188.8.131.52. Select advanced > Wipe Battery Stats > Yes – Wipe Battery Stats.
- Return to the main system recovery menu and reboot (reboot system now).