It sounds as though your battery was too weak to continue running the pump once a real load hit it. Those jacks work sequencially and the pump works harder as each stage reaches the top. My middle jacks usually won't start to pick up until the rear jacks are all the way up. At that point based on the sound of the pump, you would figure that everything was up and the system was dead heading.
I'm pretty sure I recall the instructions recommending that you either be plugged into shore power or 12v power on your tow vehicle when operating the Level Up system. It does draw a hefty amount of current.
