Usually when the wheel spins off of the ground but then stops spinning when it is on the ground with a rider on the scooter it is because of old, worn out, or faulty batteries. When you performed the battery pack load test was the scooter on the ground with a rider on it and the throttle at full position?
Some E100 battery packs have the same connector on it as the Pocket Mod scooters do, so it may or may not fit not depending on the versions of both scooters. If the battery pack connectors are identical and the red and black wires go to the same terminals on the connectors, then the E100 battery pack can be used to test a Pocket Mod.
Please let us know how it goes.