Buggy Conversion

[maxair45]

I am about to take the plung and convert my buggy to bl. I am working with some guys here to get a mount made. I am now looking to the power system. I've been reading up and have been hearing people blowing their MMM esc's and this and that. I definatally don't want that to happen. Now which if you guys were buying a bl system for you 1/8 buy? MMM? Xcellerion? other?

Also I am looking to run two 2s 5000 Mah batterys. I can just hook up a y harness up and i'll be good to go on brand new batterys right? But my question is if their used. I am saying what if i took one(one 2s pack) and ran it in my 1/10 for a race day. I don't really see a problem if I charge it up. they are both at the same voltage since their peaked right?

I am sure to have more questions.
Thanks for all your guys help.