Do I need a smart jumper?
QA friend showed me his pocket jump-starter, which seemed remarkable. Why are we still using bulky lead-acid batteries if these tiny things are so capable?
Walter Clough, via email
AThese units contain lithium-ion batteries, which store a lot of energy in a small space. When a starter motor is turned on, it briefly acts like a short-circuit before settling to a peak cranking current of, say, 100 Amps. A physically large lead-acid battery is robust enough to withstand this thousands of times – but the same can’t be said of any small battery.
You could use a lead-acid motorcycle battery on a car, but it would have a short life. The same is true of a Li-ion jump-pack. It isn’t for daily use or for prolonged cranking of an engine with a starting defect. The best way to use a jumppack is to let it recharge the car battery for a few minutes before starting. That way, the car battery’s able to do the majority of the hard work. Connecting the unit and launching into a long cranking session is likely to blow its protection diodes or and/or destroy its battery. They often don’t last long when subjected to this sort of treatment.