[Please Help Me]

I have a Craftsman riding mower, model number: 917.252541 with a Kohler 14.5 hp engine. It has run well for most of the past several years, but recently, when it is running, the charge / discharge meter is showing discharge, and the battery ends up going dead. I have to jump start it, and it usually runs okay, although, with a very dead battery, it died several times in an hour. With a newer, less dead battery, it ran until I put it in 6th gear and started to go fast. The lights work.

Does the battery have a different source of charging power than then lights? How do I determine what is causing the battery to discharge and die, and how do I fix it?

Thank you.