2014 D170 john deere lawn tractor charging problems

I have a 2014 John Deere D170 lawn tractor purchaced from the Home Depot. Ever since I brought it home it drains the battery while mowing. It does not appear to be charging the battery a s it runs. I put a new fully charged battery in it and it will kill it after only a short time. I've checked the ground to the frame and even cleaned scraped the paint and applied a light dielectric grease to the connection. Help!