Updated March 2017
Despite their very small batteries LiFePO4 jump starters really do work. This article by Collyn Rivers explains how and why. A lot of power (the rate at which energy is used) is needed. The amount of energy (the ability to perform work) required, however is surprisingly small. In the days of vintage cars, a strongish 55 kg girl could hand crank start a 4.5 litre Bentley with relative ease.
PIC: courtesy of http://www.thingsesque.com/kangaroo-jump-start
LiFePO4 jump starters really do work
There is a good reason why LiFePO4 jump starters really do work. The power required to start a 4WD engine in good working order, is 400 to 600 amps. This may seem a lot, but it’s rarely for more than three seconds.
The actual energy drawn in doing so is tiny. It is (say) 600 amps for (at most) five seconds. That 600 amps for five seconds is a mere 0.8 amp. An 18 amp hour lead acid battery thus has sufficient energy. It cannot, however, release that energy at the power level required. This is often misunderstood. If interested see: https://caravanandmotorhomebooks.com/what-peukert-really-meant/
Even an 18 amp hour LiFEPO4 battery, however, can (and will) release well over 1000 amps. They can readily be discharged at 400-600 amps. Because of this they can start a big 4WD many times.
LiFePO4 jump starters really do work – for emergency back-up use
Eighteen or so amp hours (at a LiFePO4’s typical 13 volts) is not a huge amount of energy. It’s about 230 watt hours. Nevertheless, in an emergency, half can be used to run a mobile phone or iPod for several days. Then still restart a big engine a few times.
Everything you need to know (and more) about RV electrics is in: Caravan & Motorhome Electrics. Collyn’s other RV books are Caravan & Motorhome Book, and the Camper Trailer Book. His books on solar are Solar That Really Works (for RVs). Solar Success is for home and property systems.
To quote Caravan World: ‘Collyn Rivers has put his encyclopedic knowledge into print . . . there is virtually no issue he hasn’t covered.’ Bio.