Which is the correct replacement battery?

I recently ordered a replacement battery number 616-0435 for my iPhone 3GS. I replaced the battery and checked the number at the time and am 99% certain it was the same, unfortunately I threw the old battery away. I am now having problems, the phone reboots intermittently and does not show battery usage properly - it stays at 90ish% all day then expires completely without warning. I have reset the phone but that has made no difference. The battery may be faulty but I wondered if it is possible to define the correct battery for this phone? It is model no. A1303 8Gb, is there anything which might define the correct battery?

Thanks