Oh yea, forgot about that
I only know about the newer traxxas electronics
The modern blue case XL5 esc is nimh and lipo compatible (with low voltage cutoff) and waterproof
The older Yellow case XL5 esc is not waterproof, don't know about lipo capability. - most likely can do 2s lipo, but might...
I would prefer to use a 2s LiPo
Any cheap amazon pack like
Hoovo, Zeee, gensacearespammers, CHNL, Ovonic, SMC, Liperior should be decent
2s Lipo meaning 2 cells in the battery (7.4v)
I would go around 5000 - 7000 mah to have run time. I used 5200mah 2s lipos when I still had the brushed system in...