Need some battery advice!
I'm currently having had an issue with my Interstate 12V (dual) batteries in my Arctic Fox camper, in that after 3 days of boon docking, my fridge stopped working, thus realizing I must be below 6 vol...
Forum Discussion
KX5002 wrote:
I think it's an old wives tale...
All batteries are internally wired in series. A lead acid cell produces 2 volts (roughly), in order to get a higher voltage you need to array cells together in a "battery" so a 6v battery is just 3 2v cells wired in series, two 6v batteries wired in series is 6 2v cells wired in series, just the same as a 12v battery is 6 cells in series. 2 12v batteries paralleled in my mind is the same as one very large battery of 6 cells.
Am I nuts?
Not being a psychologist or psychiatrist, I'll pass on evaluating your sanity, but I am an electrical engineer who spent considerable time testing and evaluating batteries that perform one of the most critical missions on earth so I'll try your battery question.
You are correct about the cells. The term battery has the same meaning here as it does in military use. It's a grouping of guns to increase firepower or a grouping of cells to increase voltage. It was very common in the past to have the cells individually wired to make whatever voltage you needed. So two 6V batteries in series is only different from a single 12V battery because one of the wires connecting the cells is external on the 6V pair. We used to separate batteries with bandsaw to do individual cell testing.
As far as connection two 12V or 6V batteries in parallel, there are a few "gotchas" but no general reason not to:
You don't want to connect batteries of different capacity or condition in parallel.
A parallel connection can fool the charger into overcharging the batteries a little bit because the charger keeps charging until the total charging current for the two batteries is 1A rather than the charging current for the string being 1A. This can be mostly remedied by keeping an eye on the electrolyte level which you should be doing anyway.
If you have a single cell fail in a parallel collection of batteries, you may discharge the other battery, leaving you without power, or you may cause the charger to keep trying to charge both, boiling the electrolyte away ruining all the batteries.
But if you match up your batteries and monitor them properly, the advantages outweigh the minor rare issues.
