There's nothing in the best deals thread about extended batteries, fyi.
Personally I have the HTC extended battery and I'm not happy with it. The battery life is great but at the expense of aesthetics. The phone doesn't look as nice and doesn't lay flat on a surface and will rock if you touch the screen. I find it particularly annoying. I tried modifying the stock back to get it to fit in my Incipio case but no dice, it's too big. There's a few other batteries available online (I do most of my shopping on Amazon) and so far I've found two brands of 1750 and a 1900mah version. I *believe* all of these will fit in the stock battery back.

 

I'm happy with the performance of the 1900 Mugen battery that fits in the standard battery door.

Unfortunately my first Mugen just died after Thanksgiving so that one only lasted 7 months. But I didn't realize just how nice the extra power from the Mugen was until I had to go back to my standard battery.

Ordered another 1900 Mugen and received it about 10 days ago. Hope it works longer this time, because the added battery life is great!

Check out Retail Me Not or similar sites if you plan to order from Mugen. I got a coupon for a slight discount (10% the first time, 5% this last time.)

 

2750 mAh battery & new back cover $40 - Amazon... I can't kill this battery: 100% screen brightness, 4G unlimited data plan, 5+ hours *screen on* time...

 

Not sure how often Amazon changes prices... guess you could search Amazon for "HTC Rezound extended battery" just in case it has changed.

as of 02-Jan, here is a link you could use: Amazon.com: HTC Rezound Extended Battery with Door - HTC Rezound: Cell Phones & Accessories

 

I just switched to the rezound and was wondering where to buy a bigger battery. However I do not want one that won't fit in the standard back. Is the 1900 good for that? If so how Much did it cost?

 

Right on... did you stay with the 2750 mAh or get the monster 3240 mAh?
Not going to lie -- 2750 mAh adds some heft to the phone but it was worth it to me for all that juicy power.

Like most batteries, it will take 3-5 full charge / discharge before you start seeing your longest battery life.