For example, one can order a 24 volt 55 amp hour capacity cluster with battery management board attached. The dimensions of this cluster would be 4.7 x 11.8 x 8.9 inches (120 x 300 x 226mm), and it weighs 37 lbs / 16.8 kg. This requires less space than the two AGM batteries and provides nearly triple the capacity with only 1.3x the weight. The discharge rate is from 10 to 15 amp hour Max.
I found one company selling this set for $2,200 including a specialized charger. One could scale back the Amp Hour rating, then spend less and shed some weight. I have seen 12 volt 55 amp hour packs with much higher discharge rates.
Has anybody used these batteries? Can anyone chime in?
So I think it's possible to use a LiFePo pack in our models. But the price....... 
(Here in Germany I have to pay 2500 Euro (approximately 4.000 $)) 
Perhaps I found someone with a good price. For a start I would like to use it in my 222.