I've tried every which way, but the battery charger unit doesn't charge up truck batteries. Car batteries, yes... But specifically truck batteries, no.
I've tried different battery charger units just in case it was the unit I was working with.
I've tried after a server reset in case it was some bug with it.
Tried unplugging, then re-plugging in the charging unit to the generator.
Tried a different truck battery just in case there was a problem with the one I was trying to charge.

Nothing works. So perhaps truck batteries are not meant to be charged, but that would be weird!