Battery pack/jump starter (Chorley Moor PR7)

Ring brand lead acid battery jump starter. Also useful as emergency light, usb charger and also 12v cigarette socket outlet. 33aH battery, rated at 800 amps. Supposed to jump start up to 3.5 litre engines but would not start a 3 litre diesel, so I suppose this claim only applies to petrol cars. Fully charged reads 12.75v, so should be good. It is very heavy!