I had the same issue on one of ours, put new batteries in same result, tested charging system and not charging, removed charger and opened up, there was a ceramic cyclinder fuse inside that was blown, replace and put back together worked just fine although the charger hummed very louldly, issue with blown fuse in charger I do believe was due to charger was severely rusted, mother board included, which leads to believe there may be a short in it, jacked worked for 2 months and now same result, so now I'm just going to replace the charger and be done with it, charger runs $410 on Amazon

I used another battery pack from another same model truck got same out come.It has a zapi controller.

for some reason the controller must not be able to sense the charge in the battery pack. check all power connections into the controller. Iskra controller i presume ??.i,ve seen corrosion on the terminals causing all sorts of symptoms