That battery is not nearly large enough to be practical. It's only a 4500mAh, doubt if you could get a decent charge on a single 7.4V 2S 5000mAh lipo given the practical limits of lead acid batteries as mentioned previously.

Depends on the number of charges, but you likely need an auto sized deep cycle. I used to use a lawnmower sized one back in the 1200-1400mAh sized nicad days. But had to go larger as RC battery capacity increased.