How much does SOC\Battery Balance matter in the real world

[SunDave]

This is not a hypothetical question. I have 6 Pytes 48100R batteries, in a forest RB enclosure. Pytes right from the factory sends cabling that puts two batteries vertically, and the other two sets horizontally. Basically it makes it so that none of the batteries have the same length 4 gauge run to the bus bar. Not standard connectors either so hard to swap.

Now the questions:
1. Is this actually a problem?
2. If so, how much lifetime loss am I looking at?

I could reconfigure the batteries to new positions every couple years. Or get some custom cables made with Surlock connectors and get all 6 batteries to the bus bar individually instead of in sets of two.

I have been watching SOC since I got solar-assistant. I have a rather small array, so at times when I don't get a full charge for 2 weeks, I have seen it go as far as 10-11% difference in SOC (74% on lowest battery of the 6, and 85% on the highest). If I get a full charge every few days they don't drift more than 2-3%.

There are also minor differences in draw. When the dryer is running, it could be pulling 910 watts from one battery and 880 watts from another for example.

 

[sunshine_eggo]

Each battery having equal resistance to the loads/chargers is important proportional to the magnitude of the current relative to capacity.

I would not be concerned with a ~10% difference in SoC provided you can regularly attain 100% on all.

 

[SunDave]

Thank you. Let's pretend for a moment that I am not great at digesting densely packed sentences... Because I'm not.

I have a battery capable of 12,000 watt draws, and I only ever get to 6,000 continuous. Average about 500 watts an hour over a week.
Screenshot while the dryer is going. This was after a full charge, so no SOC drift yet.


Let's rephrase and use your equal resistance wording. Is it a problem if they have slightly different resistances (see chart above for "high" draw. If so, how much of a problem. A year or two off of a 15 year battery? Or would it potentially take it out in a few years?

 

[sunshine_eggo]

Thank you. Let's pretend for a moment that I am not great at digesting densely packed sentences... Because I'm not.

Matters lots if you're pushing them hard.

Matter less if you're not pushing them hard (you're not).

Let's rephrase and use your equal resistance wording. Is it a problem if they have slightly different resistances (see chart above for "high" draw. If so, how much of a problem. A year or two off of a 15 year battery?

Maybe.

Or would it potentially take it out in a few years?

Almost certainly not.

The important thing is that EACH battery is operating within their defined specifications. Running a battery at 60A will have a shorter life than one running at 50A... how much? Can't say, but both should reach their rated cycle life as 60A is still within its ratings.

 

[SunDave]

Perfect. Thanks again!

The batteries are actually rated at 50A continuous 102A peak each. So my 20 amp load on each is not full throttle by any means. And even that is rare.

I really do appreciate you simplifying it. In this case, the single inverter limits my draw, not the batteries.