Updated 1. The stock battery seems a little weak, even for a 1300mah- is the 2150 made by the same company? 2. The Seido 1750 is a fraction of an inch bigger, but performs at least 40% better than the 1300. I have the 1750 and agree with this. I am wrong, the 3500 is a considerably bigger. 3. The Seido 3500 cover appears to be just a fraction of an inch bigger than the HTC 2150. The step size is different (Seido even steps, but HTC top step is taller), but total height is close to same. 4. Battery tests at XDA and Incredible Forums.com show performance is on par with the mah difference in size: Around 60%. added: The 3500 is bigger than I thought, after seeing some more relative picks. I guess it all comes down to how much hump you can handle for more battery life What do you folks think? Seidio is $50 and free shipping at Amazon.