2 Camper Batteries 12V or 6V

pnichols wrote:

3 tons wrote:
... this is one reason why the airline industry prefers a three or two engine configuration over a four.

Huuuuuuuuh? Something may be wrong with those statistics.

The chance of ANY ONE INDIVIDUAL engine failing is the same whether the plane has three of them, or two of them, or four of them.

As a passenger, I'd rather be in a four engine plane with one engine failed ... than be in a three or two engine plane with one engine failed.

As far as multi-cell batteries are concerned, the type of 12 volt battery failures I've experienced most in the past has been not where one cell shorts ... but where one cell goes high resistance - such that the battery voltage still registers OK, but the battery can't deliver much current for very long.



With two paralleled 12 volt batteries in an RV and with this type of cell failure in one of them, the good 12V battery will not dump it's current into the failed 12 volt battery at all because the failed battery will still have too high of an internal resistance to permit this. However, the good 12 volt battery will go right on providing current to the RV up to it's capacity. With this scenario, two 12 volt batteries in parallel is superior to two 6 volt batteries in series from a reliability perspective, because a cell in a 6 volt battery can go high resistance also (instead of going to a short). When this happens, the two 6 volt batteries in series will deliver no more current to the RV than the bad 6 volt battery can supply.

The main reason for going with two (wet cell) 6 volt batteries in series is the easy availability and moderate cost due to their common use - in deep cycle configuration for golf carts, fork lifts, etc.. Since the best type of battery for RV use is the deep cycle type, and it's difficult or impossible to find these in 12 volt form that are cost competitive to the common "golf cart" 6 volt batteries .... many savvy RV'ers eventually use two 6 volt wet cell deep cycle golf cart batteries.

We do use a couple of paralleled 115 amp hour 12 volt true deep cycle batteries in our RV. These two batteries are new, having a few days ago replaced a couple of similar 12 volt deep cycle batteries that were nearly 9 years old.