iPhone 3Gs battery dies at 30%

[RRRize]

My 3Gs is jailbroken for over a year now and it's been pretty stellar until last week. The phone just dies out when battery gets down to 30%.

Does anyone have any clues as to what I can do to resolve this?

My iPhone specs are as follows:
iPhone 3Gs 32GB
iOS 4.0.1
Baseband 05.13.04

Any help much appreciated!

 

[IrishVixen]

Download BatteryInfoLite (free) from Cydia to determine just how far off your current charge capacity is from the design capacity. Batteries lose their ability to hold a full charge over time, and the built in display meter just isn't always accurate.

If that's not the issue, BatteryDetective (same author, I think, but it's a paid app) might help you determine which app is causing the problem. While I haven't personally used it, others here recommend it highly.

 

[kbfr08]

Just go ahead and replace the battery. Easy enough repair, just follow ifixit's instructions. You need to order a 3GS battery, not a 3G battery, even though they're identical, using the wrong battery will cause issues.