I've used Li-Fe batteries for several years with no issue. Lately, I've started using Li-Ions, and like them better due to the lower voltage of LiFe batteries vs. everything else.

FYI, I found a little 2s Li-Ion battery that is 3200mha, and very small (they'll fit in any HL tank). Price is $18(US). At that price, I can use 2 in a tank if need be, but I haven't really needed anything beyond one yet. If you are wondering....the catch with any Li-Ion is discharge rate. You can't pull more than 10 amps (which is why they aren't used for cars/trucks/airplanes or helicopters) from a Li-Ion. I checked my tanks with a power analyzer, and found they pull about 6 amps (max)...even for the 20 pound ones.

So, for me, they work. Cons are that they've got an odd connector on them, but one can buy adapters for a nominal fee.