Battery drain fast.......!!!!

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http://androidforums.com – Before 3 days i bought samsung nexus i9020. i let battery to drain at end and i charge full with extra hours. first day after charge i used cellphone over internet and other programs in the end of battery about 10 hours and i make second charge with extra hours. after second charge my battery going to end for 4-5 hours without using internet , programs. today i make third charge and my battery going down -60% for 3 hours :( is normally...?? i updated android version from 4.0.4 to 4.1.1 automatically. i have standart 1440 mah battery is bad battery??? or android system spent more ba (General)