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 the data/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.