Calculating degraded battery capacity

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evertferte asked Jun 6, '23

Calculating degraded battery capacity

Hello all,

First of all, this is the setup I'm working with: 4x Victron AGM deep Cycle batteries, 12V, 230Ah @ C20. A Lynx Shunt is also present in case that helps.

I'm working on a project where we want to predict the future battery degradation using the historical battery data. Now the battery capacity is an important value in this equation. I have done some research on the workings of batteries, battery degradation, and more, as I'm still quite new in this field.

Because the current capacity is not directly stored (as far as I could see), I saw that I could calculate it with either a constant current or constant power load. However, I don't have either in my situation.

Now my question is, are there other ways I can get/calculate the battery capacity, or am I maybe doing something wrong? I'll happily provide more information when needed. All help is welcome!

Cheers,

Evert

AGM Battery lynx shunt battery capacity

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Answer 1 · 2023-06-06T18:59:49Z

Alexandra answered · Jun 06, 2023 at 06:59 PM

@EvertFerte

Calculating battery degradation with lead batteries is a difficult one (borderline an black art), as their lifespan and capacity is also affected by them being correctly charged each (as in all the chemical reaction reversed) time they are discharged, depth of discharge, operating temperatures and a bunch more factors.

Look up the PDF Energy Unlimited by Victron for more information there. It is a pretty interesting project you have there.

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evertferte commented · Jun 06, 2023 at 08:00 PM

Thank you for the quick response. I wasn't hoping to hear this, but better sooner than later. I will look into this a bit more to see if hopefully I can figure something out for this.

Would you also happen to know the same question but for Lithium-Ion NMC batteries? The focus was one the AGM battery as they are the most degraded. But we also have a few Lithium-Ion (NMC) batteries. Would it be possible to calculate the capacity for these without a constant current or constant power load?

I'll make sure to read the PDF, I didn't see this one before, but it seems like it has a lot of useful information. Thanks again!

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Alexandra ♦ evertferte commented · Jun 06, 2023 at 08:26 PM

@EvertFerte

There are two ways Peuert and coulomb counting, that could be implemented.

you could get a smart shunt and disable the Peukert.

basically it is amps over x hours. you would need a way to record the power drawn out and work it out from there. The reason why a constant load is used is so the calculation is "linear" and easy.

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