help, intellect 7 cells

i bought and rearranged the 7 cell packs for my emaxx and ran them 3 or 4 times now. On my last run the truck lost its charge very very very fast. I got less then 5 mins on it and i usually get a good 20 or so. The only thing i changed that time was i charged at 2 amps instead of 3. I also noticed one of the the battery connectors negative terminals came undone. I resoldered it, and they still died quickly. Any idea what could be going on? thanks