Battery model for 3G not found?

I was recently fixing an iPhone 3g A1241 and the customer told me the battery was not holding a charge, so I opened it up and found a model 616-0391, the only batteries I had around was the 616-0346 which used to work on the 3G, when I put the 346 battery in, the phone will not get past the apple logo, even in recovery mode it reboots and sticks on the logo and spinning wheel.

I have looked everywhere for a replacement 616-0391 battery, but to no avail. Could anyone tell me why a normal 3G battery will not work in it, and since it can not, where do I get the correct battery?