Quote:
Originally Posted by Avulon
No, they won't, they will only equalize their voltage. Once the voltage in each battery is the same no further current can flow ( a potential difference is required for current to flow, . For a typical lead acid battery the voltage remains constant from about 20% capacity to 80% capacity: so for example your flat car battery will come from 18% charge to 20% and your auxillary battery from 100% to 80%, and that's it. (take my figures with a pinch of salt, but you get the gist of it I hope).
There is a way of using a 12v battery to charge another much more than that, it needs a voltage step up circuit to increase the voltage from the charger. (that's one for the electronic engineers), I've no idea why none of these powerpacks or plug in 'emergency' chargers don't use such a system (or perhaps some do?).
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I don't know where you have got it that the voltage stays constant. It really doesn't. It stays
fairly level, but by no means constant.
The difference will cause a current, and it will flow from higher to lower until the voltages are equal.
http://www.scubaengineer.com/documen...ing_graphs.pdf