There's a pretty big crack down the back of my black 3G and its battery life is appalling. It's out of warranty now, so I'm thinking about doing a little DIY to replace the battery and, while it's open, put a new back-case on. I'm no novice: I've replaced a cracked and damaged LCD on a 2G iPhone before, and disassembled/reassembled loads of Macs working for an Apple authorised repair centre, so I'm fairly confident in my ability to follow a good teardown guide. It's just, the actual sources for these parts look pretty dodgy... I'm seeing a lot of batteries on eBay and such rated at many more mAh than the built in one. Some as high as 1800mAh, like this one. Is there a catch? Do these seemingly dirt-cheap replacement batteries actually last longer than a brand new 1130mAh battery that comes in a 3G? Or is their half-life poor? Or are they prone to exploding? I have no idea, it just seems like there should be a catch. And cases too. Should I expect a casing like this that doesn't explicitly state being an official Apple part to be an imitation? Would it actually be any worse for being such? It all seems a little suspect, so I guess I'm basically wondering if anyone here has had positive experiences with buying and fitting spare parts like these?