chubil
As we say on the East Coast "That Dog Don't Hunt".
Let's take two industrial batteries (a 36v & a 48v - flat plate - lead acid & they both meet the minimum weight required for the lift truck. These batteries are very common to a 5k sit down rider electric lift to use as an example to illustrate what I mean-

A. 18-85-24 - 36v, 85 amps/pos plate-1020 amp hr@ 6 hour rate - 23 plates/cell - 35.8kwH

B. 24-85-19 - 48v, 85 amps/pos plate-765 amp hr@ 6 hour rate - 19 plates/cell - 35.8kwH

Both batteries have the same kwH rating or equal amounts of power to be consumed and same number of positive plats/cell - this gives us an apples to apples comparison - no funny stuff with tubular batteries, changing amps per positive plate, etc, etc.
1. A 48 volt battery has 24 cells & a 36 volt battery has 18 cells or the 48 volt battery has 33% (or 6 cells more) MORE cells than the 36 volt battery.
2. The 48 volt battery has 17% LESS plates per cell than the 36 volt battery or 4 less.
3. The 48 volt battery has a total of 456 plates (24 x 19), While the 36 volt battery has 414 total number of plates (18 x 23)

The forklift run time is based on kwH usage - you pay your home electrical bill on the kwHs you consume to power all those electrical think in your home - some 110/120v some 220/240volt. You recharge the battery with kwH use.age. A battery stores that kwH capability to be consumed.

So in this example less plates actually produces the same kwH rating but there is more amperage draw (or heat) with the 36 volt system.