You're going to get a "balance board" with the B6 (or maybe it's integrated). That is where you plug the JST connector into when charging. This provides cell by cell voltage monitoring.
Basically if you have a multimetre put the probes on the different smaller wires and you can tell your cell voltage one by one (it'll be 1 and 2 for "cell 1" and 1 and 3 for "cell 2") you don't need to do this but if you wanted to know your cell voltage you can get an output that way (otherwise the other way is to get a battery analyzer to pull cell voltage readings).
Anyways, get the hobbyking battery, I ordered 4 of those batteries just this morning (although they were the butterfly/split style batteries). They're honestly the exact same as the other batteries and you'll be able to figure out how your charger works intuitively (or at least it was intuitive for me and I'm an idiot).
ಠ_ಠLess QQ more Pew Pew
READY TO >> RACE