error code 51 on 2001 GEM e4

2001 Gem e4 died and gave me error code 51. I had it towed home and charged it for 24 hours. Still nothing happening and still getting 51 code. Anyone ever have this???

Error 51 is less than 72V at controller. Check all of your batteries with a meter and make sure all of your connections are tight. Check the voltage going into the controller at B+ and B- (top posts)

Thank you I’ll check it out!!