If you needed high energy density, Lithium Ion is the highest, but the price shown seems a bit outrageous.
Clearly, the charge and discharge rates need to be carefully managed with our current technology.
Their ad sounds like they installed some internal controls.
Did you read the size and weight? I'm interested in something like that for Dragonfly. The spot on either side of the CB trunk, under the cockpit, is only about 9" x 11". I'm interested in putting a pair of 12v 150ah bats there. I'm not able to pay those prices, but BOY, I wish I could.
Also, I understand that LiFePOs get very hot and need good ventilation because of that. Maybe I could put a water tank against them, as a heat sink, and get hot (warm) water too.