Buy the bigger one, the 40 doesn't do it. I have a Mercedes Sprinter 316 (2.2l diesel),
and the 40 was not enough (yesterday). In parallel with a second booster (Fluxon) it worked.
For petrol engines, both the 40 and presumably the other boosters are sufficient (Fluxon
worked with a 3.0l petrol engine), but not in winter, near zero and below, nothing works.
Only a warm booster is a good booster...
I have now ordered the GB70, let's see if it's enough for the 2.2l diesel.

Can't understand Canziani's answer! I have already jump-started a Volvo C30 (2.4 litre diesel), Dodge Ram 1500 (5.9 litre petrol) and a Chrysler Voyager (petrol) with the GB40, without having to charge it in between! I don't know how others use the booster, but so far I have been able to start everything without any problems! The only thing I find fault with it is that the clamps are far too big!