lifttrainer,

not sure what your meaning of an OPR is but i'm assuming you mean a sitdown rider electric that uses a larger industrial battery.

Using the comparison between a pallet jack and a larger rider truck and the chargers is not really a good comparison. Most likely they charge differently due to the type and size of the battery in the machine. Not to mention they cannot be plugged into each others chargers because of the battery connectors.
Pallet jacks use an SB175 size connector usually and the full size truck uses an SB350, No way they can plug into each others chargers.

I'm sure his low voltage problem is due to some other problem like edward hit on or maybe he has some issue with a motor short drawing too much power or something along those lines. Most of the time when batteries fall short of designed runtime it is usually a battery problem though, like a bad cable or connection or bad cell(s). And i have seen where the BDI settings were not set up correctly in the controller and causing the truck to run down too quickly.

Of course your point about the charger specs might be wrong could play a part in the way the battery charges up, that was a good point to consider :o)