Below is an original post on replacing a battery for a GT200..

https://modernvespa.com/forum/topic35856?highlight=clock+battery+replacement

I opted to do the same today...after dropping the screw to remove the Front Handlebar Cover behind the glove box panel...and having to remove glove box panel to find screw...then proceeding to remove flyscreen..then removing mirrors and then removing brake pump cover...I finally got to remove the Front Handlebar Cover. Now I had to disconnect that speedometer cable and all other wiring...then remove a set of four (4) screws...then there are four (4) more screws (of which there are two would be difficult to remove and reinstall...figure I'd call it a day and follow the advice of original post and just make sure to wear a watch!

Bad News: Never got to complete battery replacement.

Good News: Found out that the screws holding bag hook (when I removed glove box panel) was loose, Speedo cable screw was loose, got to check brake fluid level, cleaned out the inside of the glove box panel and inspected wiring of previous air horn installation.

If you know of an easier way to get this replacement done I would appreciate it...thanks!