iOS 4.0.1 strange battery drain

Im very creeped about this...
let's start:
i bought my iphone 3gs 16 gb upgraded to ios 4.0.2 because of the jailbreak i downgraded it do 4.0.1,and i used it for a while and installed a lot of apps.And after some usage time i restored my phone few times and then i noticed sth when i charged it, the battery metter showed 100%,when i unplug it dropped to 95% and after some time it went up to 100%...i made a restore and then it was fixed but i noticed sth else! WHEN MY BATTERY DROPS TO 35% IT RAPIDLY DRAINS TO 26% IN 30 MINUTES WITH OR WITHOUT USAGE and after that everything goes normal...is this software problem or what!?

PLEASE HELP    

i'm waiting for sim unlock and then i'm gonna upgrade to 4.1 and i think it will be soon... i also installed battery doctor and i noticed few times it showed 29% on iphone battery meter but in battery doctor 30% wtf was that....does 4.1 have sim unlock