Something prompted me to at last enter my memo pad battery log into a spreadsheet.
It generated some numbers that might be informative.
System: X5304 R, 72V 48A Xlyte SI digital controller, 2 X 24V, 18Ah, Nexcell NiMH in series.
Bike: Mixte MTB with Xtracycle. Rider: 150 lbs. HIlly terrain...