Over the years I’ve jumped my lawn mowers, jet skis, and motorcycles using my vehicle with no trouble. Last night my neighbor could not get his mower started and asked me for help. The battery was low and turned the mower over very slow. I pulled the plugs and poured a little gas in each and then jumped it off of his truck. It fired up and ran great. We let it run for a while (1/2 hour) and then turned it off. When I went to start it again the battery was completely dead. I mean nothing. Prior to jumping it, it would turn over slow but now it wouldn’t even turn on the lights. It’s a 12 volt system so what gives?