If it fails, you won't be able to boot the game, so JJP recommends it be replaced every 3 years. You also have to replace it with the machine on, otherwise again the game won't boot. There is a little tab on the bottom. Gently pull back on that, and the coin battery should lift out with the tape. It took me a few tries before I noticed the tab. Don't force it. If you find the tab and gently pull back, the battery will lift out easily.

Mind the whirling open fan next to your fingers! I cut myself on it.

There are instructions in the manual that talk you through it. Unfortunately, the instructions don't mention the tab or the fan blade (did I mention I cut my finger?).

It is also not just about losing your settings. If you replace the battery without the power on, you won't be able to boot.

There’s a way but I think you need to hook up a keyboard to the computer and do magical computer stuff. JJP can talk people through it I believe. It just isn’t a hassle you want.