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Your smartphone's stock battery sucks. I'm sorry, that's just the truth- no matter what phone you buy. The Evo can barely survive a workday of moderate use. The iPhone 4 is much better, but every person I know who owns one brings their charger to work or keeps one in the car at all times. The things we like to do, browse the Internet and watch videos and use navigation apps, are all battery intensive.
The problem of crappy battery life is compounded by the fact that a dead smartphone is worse than useless. We come to rely on instant, persistent Internet access and the power of Google Maps. A dead smartphone is like losing a sense.
So, there's good reason to spend a little extra cash on an extended battery.
Case-Mate's new iPhone 4 Fuel Lite launched earlier today. It adds 4 extra hours of talk time or 5 hours of video. That's 240 total hours of standby for $59.99. You could also go with the iPhone 4 Fuel Max, which adds 9 hours of talk time or 10 hours of video (300 standby) for $99.99.
If you don't mind looking nerdy as all hell, you can always try the WXG Fuel Extended battery pack. This baby works for the iPhone 3G and the 3GS. It contains a 2200 mAh LiPolymer battery that offers triple the talk time. There's a power control that allows you to set when you want it to charge your iPhone. Basically, this thing turns your waist into a power outlet for $49.99.
Here is a link to all the extended batteries you could possibly want. It includes Seidio Innocell batteries for the HTC Droid Incredible and Eris, plus 2600 mAH batteries for the G1 and 1750 mAH batteries for the Evo and Hero. Most of these will run you around $50.
The 1750 mAH is nice because it provides more battery life without expanding the actual size of your phone. The Evo is pretty damn big as it is. If you ARE willing to sacrifice size for longevity, this 3500 mAh battery is frankly amazing. You can also find one for the Incredible.
First off, this Tekkeon Charger works on RIM devices and provides some extra on-the-go juice. For more permanent solutions, you'll want to try something like this 2600 mAH Seidio extended battery for the Curve 3G, 8530 and 8520. $59.95 buys it, or for $49.95 you can get a 1700 mAh for your Storm.
Ten hours is a lot, but sometimes you just can't afford to stop and charge. Those times justify the Kensington PowerBack battery case. It gives 5 hours of juice, bumping your iPad up into a 15-hour power monster. $129.99 is a steep price to pay, but you'll be glad you have that extra 50% when you end up stranded in a foreign airport with no plug adapter.