nimh or lipo or other?

[suicideneil]

For BL I would recommend lipo (lithium polymer) or A123 (Lithium ion), but the lipo cells will most likey fit better than the funky sized A123 cells, and you need to run them in a 2p configuration to prevent the voltage from drooping baddly under load.

Reading material

For 4s lipo, I would suggest either the 8XL or 9XL in a heaver savage- 8 for speed, 9 for runtime. As for escs, well, depends what flavour you like really, but the MGM 120-18 is a safe bet; you ideally want to have some headroom in the voltage department so that the esc can absorb voltage spikes and such without going thermonuclear on you. $180 is a great price for a 6s 120 amp esc, or you can try the MM esc as that will do 4s and 100amps, but ideally needs a few mods like an extra capacitor and external UBEC.