Flat battery

[SimonB]

With a power pack you can be totally independent of others. Useful if you are wild camping or have parked where it is difficult to get another vehicle to help with the jump start. They also take up less space than a set of jump leads. They are about the same size as a box DVD set.
It can be used to charge some of the gadgets that we all have these days, phones, tablets, etc as well.