Its not metal as that would short out the battery. Its the coating onthe plates that has fallen off and with a little lead coating. It happens almost all the time. It sounds like you have one shorted cell in the battery and there is a lot of different batterys out there to replace it with and it depends on what you do with the car. Big stereo ect. Just make sure you get a battery that will fit good in the holder and with the posts in the right direction. I have seen too many people put a battery in backwards and not the posts are close to the core support. Usally you will want a battery with a R after the battery number witch means reversed poles. Heck I can't complain on my battery from Honda as its still the original and like the energizer bunny just keeps on going.