TN BRAND LITHIUM LEISURE  CARAVAN CAMPER VW T5 etc  AH LIFEPO4 LITHIUM IRON PHOSPHATE BATTERY.
Upto 7000 cycles to 50% capacity
Will do 100% discharge repeatedly without damage.
These use grade A cylindrical cells and are expensive units to buy at around £500.
Much liked by the marine/ boat users. TN do sizes from wheelchairs to big trucks
Aughton, Lancashire