definately check the battery, 48v is low (discharged).
dropping to 44v is a pretty severe drop.
a fully charged 48v battery should be reading over 50v if in good condition.
run a check on each cell and i think you'll find some cells bad.
given all the different codes it is throwing out fixing that battery would be the first order of business.
If you have another good battery, check it out and put it in the truck, this would be the quickest way to rule out the bad battery.
If not then you'll have to run a charge on the battery and then retest.