which battery chemistry is best for solar charging?

[Rusdy]

...and there is nothing comparable that I could find. Its a solar charge controller custom made to my 36v (41.8v) LiFePO4 battery pack... or can hack the controller...

I'm with you there. I had the same problem trying to find lithium charger for my e-Bike battery (36V Lithium NMC) from my 12V panel. I had an absolute bargain when I bought the panel and didn't realise there is no charge controller for it. Genasun one is really too expensive for me.

So, being a stingy b@st@rd as I am, I designed and built one from Arduino. Not as top spec as Genasun of course, but worked well. I've been using this in the last couple of weeks, and worked really well. I'll keep update for the improvement (to increase efficiency)

Details:
http://epxhilon.blogspot.com.au/search/label/Electric Bike