New to forum and GEMs 825

Have a customer’s GEM E825 2000 model. Been sitting for about 1 year, batteries bad. replaced all batteries and the only way to make it move is to turn key on (contactor snaps in then back out), then turn on turn signal (or anything 12v) for the contactor to rengage, then drive. The 12v stuff will not work properly (wiper takes 7 min to cycle). I thought it was the dc/dc converter but we installed a new one. With the new converter in, it will not do anything. It has a QuiQ 912 charger that someone installed. I hooked the red/green wire together and it is back to what it was doing before. PLEASE HELP I need this thing out of my shop!!!