I think he has described and priced replacing every cell in the industrial battery that this truck has.
however battery prices have climbed pretty steadily in the last decade or so, so a $3.5K (1/2 the price) new battery would be a pretty good inexpensive battery.
we might explain here that the reason NOT to use the smaller batteries is that this truck uses the battery weight as a counterweight, so using much lighter batteries seriously diminishes the unit's stability and lifting capacity.