I just bought a used 2007 450 grizz. I test drove it at guys house and it ran great and I took it home. I brought it to brothers and we were looking at it and I tried the winch while machine was running. It winched out but as soon as I tried to winch in the machine shut completely off and everything died. I turned the key off and on and nothing. I pullstarted it and the dash said I was going 8 mph and jumping all over when I wasn't moving. I put it in reverse and it sputtered and backfired. I drove it down the road to my house and the reverse light was flashing. I'm new to owning an atv this is my first. Is it most likely a bad battery? Any help would be much appreciated.