The whole Li3 issue of $20K sort of irritates me anyway. I do this stuff for a living. My last design has an Li battery and smart charger. The battery pack contains all of the safety circuitry as well as the battery. This is the only way to get them these days for safety reasons, i.e., Samsung phones. We buy the battery pack for a little under $2.00. The charger we buy from Linear Technology for 95 cents. There are a few cents worth of resistors and capacitors in the circuity. The charger rates are controlled by a small micro controller that cost less than $3.00. The case of the design doubles as the heat sink. I wrote the firmware that monitors all of this in less than 4 hours. So, this is small battery (2.7Ahr) and charger (1A max) for a small system, but all the electronic principles are exactly the same. If you scale it up to a 400Ahr system, it is nowhere close to even $2K. Just how much money do the RV builders need to make? I bought the resonator form Cummings. It does cut the higher frequency barking of the Onan quite a bit.