BlackBerry 8830

I am still new to the BB and liking it a lot but I can charge the phone and it tells me that the phone is at 100% charge, then after a few calls maybe around 20-30 minutes total of talk time the battery goes down to 2 bars or 60% full? I usually wait until the charge goes down to 20% to charge the phone, maybe I’m not charging it long enough, 4-6 hours or overnight, during the charge the phone is set to turn off at 12 p.m. and start up at 7 a.m. I never noticed if the light turns green telling me that it is full, I just check to see if there are full bars then go to the options>status to see if the battery is up to 100%? could it be the battery or may I am not charging it long enough? I know I read that the phone can have a last time of...
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