You buy an extra battery? Trying to decide if it's worth the $15...
I got an extra battery back when I got the big accessory pack. I think I paid $30 for the pack back then. I hated the case, and don't use the colored back. But it was a good price for a spare battery and A/C adapter. Also included a screen protector, which I don't use on my Thrive
Anyway, I think $15 is a good price for the battery, it's $23 on Amazon and gets 5 star rating. I haven't yet had to replace my battery, but I LOVE having the option.