dead battery

The battery on my 2004 tdi90 was flat so I used a fully charged Halfords portable 2L lithium ion jump starter for the first time. The instructions ask you to connect the positive jump lead to the positive terminal of the dead battery and the negative to a suitable unpainted point on the chassis...

I haven't used the car for 10 days and when trying to start - nothing no lights. Multimeter showed 10V. Already have a new F18 Varta on order but I tried to start the car with one of those jumper battery packs (Suaoki G7) and it wouldn't have it. Cranking for a second and then all lights off...

Hi, I'm trying to charge up my dead battery in my A2, however, the battery jumpstarter I have does not have cables long enough to attach to part of the chassis. In your experience, what is the best battery charger/jumpstarter to get my A2 running nicely again? Thanks