Recently I noticed that my phone goes dead at 30% and will not turn on unless I plug it in. I have ios 6.1 jailbroken. What is up with this?
Have you tried recalibrating the battery? By that I mean letting it drain until it turns off and then recharging it fully before using it again.
The best way to keep your battery calibrated is to only plug it in when it goes under 20% and then to charge it completely to 100%, without interruption.
If you keep doing "shallow charges", ie. charging your phone when it's like at 50% or higher and then unplugging it before it hits 100%, the charge meter will become slowly inaccurate over time.
As mentioned above, best way to recalibrate it is to let it run out completely and then to charge it overnight to 100% and just leave it charging for a couple hours.
The phone will automatically activate "trickle charging" when it get's to 100% so it never actually overcharges your battery anyway.
guys not to sound like a dick but he/she did mention it shuts off at 30% so how can they recalibrate it if it dosent go down to 0%