I don't have solar or wind charging. "Charge controller" is a misleading term, what I should have said is "Battery Management System".

LiFePO4 (Lithium Iron Phosphate) is a new battery technology that offers much higher charge densities, over 2x that of conventional lead acid, AGM or gel batteries. A 200Ah LiFePO battery for example weighs about 55 lbs, compared to the ~120 of the Mastervolt. They can also be deep discharged down to 20% or so without any problems, and unlike lead batteries they provide a stable 12.8V continuously until discharged.

LFP batteries are much more stable than the LiCoO2 batteries used in cell phones, etc (you know, the ones that on rare occasion catch fire in people's pockets). The downside is that the danger of overcharging or over-draining is high, and thus they require a Battery Management System, a controller that regulates charging and equalizes charge between all of the individual cells that make up the battery, and also ensures the cells never drop below a critical level of charge beyond which they can be damaged.

At the moment, these BMSes are fairly DIY, and the batteries themselves are a little pricey as well.