[Flibmeister]

My bet (and I mean that literally, since I ordered one) is that the 1350 mha is a typo, and it really is an OEM 1340 mha battery. I've seen reviews of the phone that state it has a 1350mha battery, too, so it's a fairly common error. If it isn't an OEM battery, the seller is deliberately misrepresenting the product-- and since he has a pretty high feedback rating, that doesn't likely.

FWIW, I have a spare battery that I bought directly from HTC (that has a slightly different part number than the battery that came with the phone, BTW), and it cost almost exactly double what this ebay seller is asking.