I will do my best to describe this so bear with me. The ATV is a Chinese make but the make might be immaterial with this problem. I have now gone through three batteries in a few months and the last two just a week apart. Here is the sequence:

I use my atv lightly almost every day but that is only about 5 months a year as I live in Florida and Michigan and the unit stays in Michigan over the winter. I always store the unit and trickle charge the battery, and this does not seem to be the issue - let me explain. Last fall, just before I left for Florida, the battery died and it was a few years old so I wasn't concerned. It did die without a lot of warning as I didn't get the gradual slowing of the start process that usually precedes the battery death, but I didn't think much about it. It died completely and would not take a charge or a jump so I bought a new battery and it worked great. I only drove it once or twice and then put it up and left for Florida. Came back a few weeks ago and the battery was in good shape on the trickle charger. Put it in and everything went well...for about a week. Without warning the battery went dead (10.8V) and would not take a jump or charge. Like the previous year there was no gradual wearing down, it just quit. I chalked it up to a cheap battery and got another battery. This one was strong and the atv started up like always...for about a week. Same thing with no warning and this time the battery was at 11.4V. I'm thinking bad alternator/rectifier, at that time but I needed to check it. I charged it, though it again did not seem to want to charge, at first, but then I got it to 12.6V so I gave it a shot. The minute I turned the key it died - no starter sound at all. I jumped it with my tractor and it started. I immediately put a voltmeter on it while it was running and it was up around 14.4V which tells me the alternator part seems to be working. I let it run for a bit and shut if off. Next morning...dead (11.4V) and struggled to take a charge but I did get it to 12.6V again so I went to hook it up. Put the positive cable on first and just for kicks I checked the voltage before I hooked up the negative cable and it was 11.3V - just from hooking up the positive. I got another older battery to take enough of a charge (12.8V) to try it again. This time I hooked up the negative first and checked the voltage - 12.8V still. Hooked up the positive and checked the voltage - 10.8V. This makes no sense. Simply connecting the positive cable completely kills the battery without ever turning the key or anything. And when it kills the battery it really kills it. They usually don't want to take a charge so something is really busting them.

I am at a loss...thoughts?

 

Put a good battery on, only connect one side. Connect other battery post to a fairly heavy duty ammeter and connect loose battery lead to ammeter. Ignition off, does the ammeter show any reading? If it does, disconnect the regulator and see if the reading goes back to zero. If this cures the battery drain, fit a new regulator. If removing reg doesn't cure the drain, disconnect key switch. If this cures the drain, fit a new key switch.