I found a video that may help you out.
Snarlingrabiddog on youtube has a video on the replacement.
It is a bad clock battery, they are rechargeable and have a finite life.
If you are very gentle you can get the case apart with a screwdriver. But if ordering the battery from Moto, get a gasket and the tool while your at it. I recommend you lube the gasket if reusing the gasket, and clean the gasket surfaces when putting it back together. Also helps hold the gasket in place and makes it much easier to get radio back together. And will help it seal better if not replacing gasket. New gaskets come prelubed.
Side note, just incase FFPM571 jumps in here or any one else.
If you don't feel comfortable using a screw driver, than by all means get the tool.
I have opened tons of these radio's with and without the tool and have not broken a case, (keyword) YET. Knock on wood.
I have had other techs still break the case even with the tool. Be gentle whatever u use,