The Juno Power Jumpr does what most other portable device chargers do, namely provide power when electricity is scarce, if with the addition of a further power-- jump-starting cars in times of need.
In fact the 6000mAh battery delivers a 12V output at peak 300A via dedicated port. According to Juno Power this allows it to jump-start most 4- and 6-cylinder engines. No such luck for your V8, though.