With your FRA membership you get a heavy discount on optipower lipo batteries. They do also sell chargers and psus but you may be cheaper going elsewhere.

Lipo packs come in various cells counts (like the days of nicad/nimh) denoted by the s value (3s, 4s, 5s etc). The C value tells you in multiples of the pack capacity what the discharge rate of the pack is. Generally there is a constant C value and a burst rate which is much higher. For example a 5000mAh pack with a cont. rating of 20C can discharge 100A constantly (5x20). You will generally find a max charge rate in the same units. When charging, you need to make sure that you use a balancing charger to keep the cells voltage close to one another. If one cell goes too far out of range then it can destroy the whole pack.

You must also charge lipo in a lipo sack (find them for a few quid on ebay) as a safety measure. If the pack decides to go up then it keeps the fire damage contained.

I realise this all sounds very nasty and negative but the power available from lipo for the weight is incredible. If you are running any kind of high power motor on a disc for example then you will notice a huge difference when compared to SLA.