Puffed my Lipo today

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Would too low of gearing draw too many amps thru my batteries? I've been messing with my Maxx for awhile now, and thought I had everything worked out until I pulled my batteries off today and one smelled terrible, puffy, and 185f!!! Only one pack got that hot, the other was only 140f and no puffy. This was after 20 minutes running on a track.

I'm running 2 x 2s2p 6000mah TPs, 9920 and 7XL. I have UE diffs, Gmaxx single speed, big tires and 12/51 gearing. I was trying this gearing because I was having problems overheating the ESC, but since I put a fan on the ESC runs cool. Motor temp seemed ok at 150f after 20 minutes, I was going to try 14t pinion next, but batteries are gone. :(

So, now I'm wondering if 2 x 8000 2s2ps would work ok? Since one pack seemed to draw down more than the other, I figure I should run a Li-saver on each battery?
Since I have a 9920 with dual deans plugs, would I just run one off each deans plug? Or would I hook the Li-saver right to each battery?