To prevent that my refrigurator is running out of power I want to add an extra battery. I still have an 110ah available anc currently using a 130ah. Both Victron Energy gel batteries.
asked
Can I use a Victron Energy gel 110ah & 130ah simultaniously for a 2x140watt solar system?
It is definitely not recommended.
you can parallel a new battery with your old one, but as soon as you do the new battery will take on the same age and capacity characteristics of the old one
Thanks Marc-Heid that's indeed not something which looks positive. So in case both batteries are still having an 100% capacity; would the 130ah then reduce it capacity to 110ah?
Regards,
Pieter
It doesn't reduce the capacity of the bigger battery. But if you assume that both batteries deplete at the same rate, the smaller battery would be over discharged by using the full capacity of the bigger battery and badly damaged. So there's an effective limit on how much you can use of the bigger battery's capacity.
There are considerations about charging as well. And the bigger battery will tend to carry more of the load.
AGM batteries should not be discharged more than 50%, so you're effectively making a 110Ah pack. And as already said, not recommended. But the batteries are pretty close in capacity, so as long as you don't discharge too much and make sure to charge well, it will work, but sub optimally.
I think capacity of this parallel set of batteries (110 & 130) will be the sum of the capacities. 110 +130 = 240Ah. The smaller one will not be over discharged because SOC in LA batteries depends on their voltage and the battery with higher SOC will keep the voltage up for the smaller "neighbor" until its SOC is done.
Batteries are chemical reactions producing constant voltage. The speed at which this happens depends on their internal resistance. A fresh battery has a low resistance, but this increases as it wears out. Joule’s law dictates that thermal energy gain accompanies loss of electrical energy.
Thus, mixing old and new batteries forces an excessive amount of energy through an abnormally high resistance. The new batteries run out sooner, while the old battery overheats. By mixing old and new, we are wasting good money. This applies to mixing older and newer fresh batteries to a lesser extent.
If the batteries are in parallel, which they will be here, the new battery simply takes more of the load.
But we have no information about age, just the capacity difference.
OP said load is low. Probably ok here as long as light use.
