iPod 5th generation 30GB Model MA002LL/A or A1136 battery type

I am shopping for a battery replacement for my iPod 5th generation 30GB A1136 Model MA002LL/A.

I have found on sites like iFixit and eBay various offers, but would like to get the correct mAh. All offers for that type of iPod offer 3.7 Volts, but the vary from 580 to 650 mAh. I am replacing my hard drive with an iFlash Quad MicroSD Adapter.

Which battery replacement should I buy?

Thanks and regards.