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
BFL13 wrote:jkwilson wrote:BFL13 wrote:
"You don't want to connect batteries of different capacity or condition in parallel."
Yes to condition, no to capacity. No problem paralleling different capacity batteries. They charge and discharge in proportion. They maintain the same voltage and SOC.
The charger tuned to stop at 1a per battery would stop at 2a on the pair.
The problem with paralleling different capacity batteries is that the discharge curve isn't linear. Once you draw a certain amount of power, the smaller of the batteries can become a load on the larger. It will work, but you don't get the capacity increase you might think you are getting. Your actual capacity will be close to two of the small batteries in parallel rather than the sum of the two.
My Trimetric shows otherwise, but I am off camping so will not be able to continue this for now. Maybe some others can chime in.
Actually adding the two gets you more than their total, in effect, because of Peukert, but they still remain proportionate.
I wouldn't disagree that they can play nicely together, but for the average user two identical* batteries are less prone to pitfalls. Often a smaller battery uses different plate geometry which can affect internal resistance when new and the rate at which the battery ages.
*The differences in batteries off the same production line can be pretty profound. I used to spend days measuring internal resistances of hundreds of commercial batteries to assemble a stand-in for a large high voltage battery bank before we thought to specify internal resistance when we purchased.
