If you can't change the battery in your Boxster, turn in your man card. It takes a type 48 battery, which is smaller than the stock, but just as many cold cranking amps. Open front trunk. Remove battery cover. Remove positive than negative cable. Remove hold down. Get in trunk and lift old battery out. Put new battery in. Move hold down clamp up to new battery and bolt down. Reinstall clamps and cover. Go have a beer. Takes about as long to do it as it took me to type this.
More details and what batteries fit can be found at Mike's site:
https://sites.google.com/site/mikefocke2/batteries