I have a 2014 Sightseer in which the coach batteries(2 6v) dried up quite a bit. Once I filled them with distilled water, they eventually charged up to where there was enough juice to start my genera...
First, replace the batteries, there toast. Second determine what converter/charger you have. Third, find out if it is working correctly. If not, replace it. Fourth, read and learn how to maintain your batteries.
The fella thsy said he only gets three years out of his batteries is definitely doing everything WRONG. Do not follow his advise. Most people get 6+ years out of a battery with minimal care.