My battery is not charging on the L120. I jumped it off the car and it ran fine. Started to mow with the blade engaged. It ran for about 2-4 minutes and then the blade disengaged but the motor was still running. Took it back and jumped it. Blades engaged and then it disengaged 2-4 minutes later. Any one have this situation. I think it is the battery as I put it on the charger and tried it again after charging and it worked fine. Still won't hold a charge though. Any suggestions?