Hi

This is a soldering job, if you are OK with soldering then go ahead, if not you need to get someone to do It for you.

You need a Panasonic BR-2/3AE5SPN 3Volt Lithium Battery to replce it, they usually last around 15 years.

If you are in USA or Australia then you can get no problem.

If UK, the you can get from Cell Pack Solutions in South Shields, they will modify the BR-2/3A with the single pins each end of the battery, just doing this to mine now.

Good Luck

Alan