I think it's probably far better just to leave the battery in your phone. You'll have to replace it after about a year or two whether you use it or not anyway. They all fail in some way eventually. Always.

I'm not sure if things are the same where you live, but in Asia you can buy an original brand new BL-5J for about $15 USD. Easier just to replace it. If you want an identical battery from a 3rd party, then you could get one of those for about $3 to $5 USD.