Some clarity for wire sizing for 2nd leisure battery
Posted: 21 Aug 2025, 16:33
Hi guys. I just read through this thread: viewtopic.php?t=176547
There seem to be two schools of though though which seem almost equally popular.
The one is to gauge as low as your max expected draw of the fuse block total loads.
The other is gauge it to be close to the max charge rate of the batteries, meaning thick wires.
I think I will go with the latter as belt and braces and it is only going to be a tiny cable length since they will be right next to each other but the first one seems strange to me? I get that once out of the battery circuit you would only gauge the wire out to the fuse block at that rate but don't really get how the wires between the two batteries would not be greater than than the loads of the appliances? Doesn't the other battery count as a load so in some cases there could be a large discharge between the two? meaning thicker cable would be better.
Anyway, regardless I will be going with fat cable of 170A I think as that is what 12V planet recommended and also battery support. Btw I have one lifepo4 @ 100Ah and want to add another, with them having 100A - yes that is A not ah! max discharge. So I had been going on the assumption to gauge for the max discharge + 25% buffer so 170A continuous cable from 12volt planet is the closer one. Better to overshoot than under.
Besides my own considerations the comments in that thread above about equalizing charge between batteries as a reason to use thicker cable which is a new rationale to me but seems sensible.
There seem to be two schools of though though which seem almost equally popular.
The one is to gauge as low as your max expected draw of the fuse block total loads.
The other is gauge it to be close to the max charge rate of the batteries, meaning thick wires.
I think I will go with the latter as belt and braces and it is only going to be a tiny cable length since they will be right next to each other but the first one seems strange to me? I get that once out of the battery circuit you would only gauge the wire out to the fuse block at that rate but don't really get how the wires between the two batteries would not be greater than than the loads of the appliances? Doesn't the other battery count as a load so in some cases there could be a large discharge between the two? meaning thicker cable would be better.
Anyway, regardless I will be going with fat cable of 170A I think as that is what 12V planet recommended and also battery support. Btw I have one lifepo4 @ 100Ah and want to add another, with them having 100A - yes that is A not ah! max discharge. So I had been going on the assumption to gauge for the max discharge + 25% buffer so 170A continuous cable from 12volt planet is the closer one. Better to overshoot than under.
Besides my own considerations the comments in that thread above about equalizing charge between batteries as a reason to use thicker cable which is a new rationale to me but seems sensible.