Tried a smart lithium pack and the tow truck guy tried a huge dumb pack, neither would work. I assume the battery was just pulling too much and the DC to DC was balking. We did not try completely removing the 12v but that's a good idea in a pinch. I've read there can be issues if the jumper pack is too smart and doesn't provide continuous voltage. I think they said the DC to DC has to see over 9v for a bit for them to close.