Originally Posted by OnceBefore
Did you charge the jump starter? It might not have a full charge out of the box.
That's also what I'm thinking. Secondly, how are you hooking it up? A lot of people do not know how to correctly jump start a vehicle and hook the good battery/vehicle directly to the bad battery/vehicle.
The correct way is to go from positive terminal to positive terminal.
Negative Terminal on the running car / good battery,
GROUND the negative clamp on the dead car - like clamp onto the alternator bracket or some kind of bracket on the engine. Do NOT connect to the battery.
You're not trying to "recharge" the battery, the idea is to give power to the dead vehicles' starter so that it can start and let it's own alternator recharge the dead battery.