Pros: No self discharge, no memory, about 1/2 the weight of NiMH, non combustible, and non-explosive (unlike it's cousin, Lithium Polymer batteries), about the same cost as a NiMH of comparable MAH, super high MAH available and a life span of 1000 + cycles without capacity deterioration.

Cons: Don't let them fully discharge, or they are ruined, and the lower voltage per cell (3.3v) makes them bad for power hungry applications (such as racing), but just fine for tanks.

Charger: You'll need a modern charger to charge them up. LiFePo4 are 3.3 v per cell, and top out at 3.6v per cell. Some Lipo chargers will work IFthe charge voltage is adjustable down to 3.3v (from a LiPo's normal 3.7v). We had to upgrade to a new charger (Thunderpower 610C) which we bought for $60 US used. The TP 610C has computer upgradeable (downloaded for free) firmware to accomodate changing battery chemistry. Balancing chargers are recommended, but you could easily use an external balancer as well.

We bought some 8400's from HobbyKing http://www.hobbyking.com/hobbyking/s...dproduct=14072 for our Tigers. These are slightly longer and fatter than a stock NiMH 6cell 7.2v stick battery. The 8400s fit just fine in our Tamiya Tigers and King Tigers. We had to change the plug out to a Deans (we do this on all my batteries) The 8400s cost about $55.00 (US). the 4200s cost about $25.00(US). At $25.00, they cost about what a comparable NiMH 4500 battery costs.