I've yet to restore mine - though I've had to reboot it a few times.
Next time it goes wonky, just reboot it. It's usually a matter of locking/unlocking it twice, then holding the up & center buttons down until the logo pops up. After reinitializing itself, should be OK.
According to Apple they are not... according to a lot of other people (myself included) they are.... it is pretty easy to find replacement batteries, instructions and the tools to open one up and do the job.
I replaced the battery on a dead one that was out of warranty for $20.