Hello, I have a 4‑year‑old 6V battery bank and I would like to add a second battery bank. To avoid reducing the lifespan of the new batteries, I’d like to know if this setup would work
no.
two 6v batteries in parallel = 6v.
what voltage is inverter?
One battery represents two 6‑V lead‑acid batteries in serie.
It a multiplus 12v 120v 3000
Depending on how hard the existing batteries have been cycled, they may be past their best.
Always best to pair like for like / age for age, due to mismatched capacity / discharge rates / recharge rates ect.
Have you considered going lifepo4, cost of two 6v lead acid batteries may be about the same as one lifepo4 12v.
Remember when sizing a lead acid may only have usable 40% DOD, lifepo4 has at least 90% DOD ( 80% if you want to be conservative).
So lead acid 100ah may only have a useable 40ah.
Lifepo4 100ah useable 80ah and should last longer.
“The problem with a lithium battery is the cold. My system is at my cabin, and it’s only heated when I’m there. So the temperature sometimes drops to -30 °C
Lithium also wont discharge rapidly when in the cold. Maybe look at getting some heated batteries.
4 years is “old’“ for AGM batteries. I see you are trying to save money but don’t do that plan.