How much battery do I need?

[othello]

A Kontronik Jazz 55-10-32 would fit. Up to 43v (10s lipo). 12s A123 would settle quickly below 43v when fully charged. Integrated car program with proportional brake and reverse. The ESC is listed for 55A and 65A for 10 sec. Heli guys do see peaks of up to 120A with 10s = 4KW. At this power levels proper cooling is needed.

I am using this ESC in my 1:8 buggy with 10s1p A123 without issues and it gets only warm to the touch with peaks up to 1600 Watt.

Another option would be to use a flight ESC with a brake servo. HugeOne is using a CC phoenix 85HV in his 12s 1:8 buggy. See this thread.