I purchased this waverunner several months ago from an individual who had just had it winterized and a new battery installed. I kept a battery tender on the battery at very low voltage. However, when I went to start the ski a week later, it was dead. I hooked a remote starter to the ski and it ran fine as long as it was running off the battery pack. When I unhooked the battery pack, the ski shut off!! Can anyone tell me what might be killing or draining the battery and why it won't run on it's own after it is started?