I know it was stated above about amps but it was calculated wrong.
Batteries in parallel the voltage stays the same and amps are the sum of batteries.
For batteries in series, the voltage increases for sum of the batteries, and amps stay the same.
Example 3 batteries in series make 36 volts; if all 90 AH batteries, you still only have 90 amps. Of those 90 amps, you can use 45 amps before you get a voltage too low.
So, a 100 amp littium would give you more than double the run time.
It is easy to get series and parallel rules mixed up.