Attaching a fuse to a new set of batteries?

pnichols wrote:

DrewE wrote:
A short would presumably be a single shorted cell, not a dead short across a single 12V battery.

Well ... current flow rate is all about the potential (voltage difference) driving it and the capacity of the potential source to supply the rate.

I worry about one battery going bad and having one shorted cell such that it becomes downgraded to only a 10 volt battery. Hence (with, say, two originally 12 volt batteries in parallel) you would then have a 12 volt good battery with a capacity for supplying maybe 1000+ instantaneous amps across the 2 volt potential difference created by the 10 volt bad battery "load" in parallel with it.

I wonder how much heat and/or gas pressue a 1000+ amp current flow driven by 2 volts can create?

If my fears are justified, I guess it might be a good idea to fuse between paralleled RV batteries ... just in case.

A 1000A current with a 2V drop is 2kW of power being dissipated, so under those conditions there would indeed be a lot of heat.

However, I'm pretty sure you won't get anywhere near 1000A, as the battery with the shorted cell won't charge at that rate with a 2V supply above nominal (and the voltage in the good battery would also sag more than 2V quite quickly with that amount of current). Exactly what charge rate and hence current flow you'd see depends on lots of things, such as the batteries state of charge and the ambient temperature. It seems to me it should in general not be all that far off from an equalization charge, which of course doesn't generally result in extreme collateral damage.

If you generally see these levels of current readily from a two volt difference between batteries, we'd see jumper cables get vaporized, or at least overheat, on a fairly regular basis.