bent battery cover

Looks like your best option would be to obtain a replacement thru Apple - either by going to an Apple Store or Authorized Service Provider, or by calling AppleCare at 800-275-2273. You might also be able to order a replacement via online self-service - http://www.apple.com/support/serviceassi...

All of these options will maintain your warranty, and depending on the situation resulting in the bending of the cover, may be at little or no cost to you (Mac Genius will be your best bet here, as they can probably be convinced to cover the part under warranty...)

Hope this helps!