If you can afford a Storm, a Tour or a 8900 you can buy batteries. Battery life and rushing to find a car/wall charger becomes a non-issue and gives you a liberating feeling. Go here and check it out.
Link: Lithium Battery For Blackberry Curve 8900, Storm 9500, Storm 9530, Tour 9630 - BlackBerry 9630 / Tour
Highly recommend you get your batteries from this place. I have a Tour 9630.
But...when I had my 8900 on T-Mo, I bought three batteries for $11 a piece. They're not OEM. But, they are the 'DX-1' size the Storm, Tour and 8900 all use.
Now...in the interest of not turning my shiny new Tour into a doorstop, I invested in the OEM DX-1 battery in the Verizon store. Those (and the one in the box) are 1400mAH.
The CellPhoneShop models are 1250mAH and hold slightly less charge ...but are invaluable if you need that boost to get you through an afternoon or overnight/hangover/wakeup period.