Extending battery life by periodically limiting SOC

Ampster said:

Does the battery have memory or does the coulomb counter need recalibration every once in a while?

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This chemistry does seem to exhibit a type of memory effect, at least if we can use that phrase generally to mean a change in the shape of the charge curve.

I can see it during my charges at around the point where I tend to float the battery when not in use (in the middle SOC). There is an obvious bump there, in what would otherwise be a pretty perfectly-linear regime:



What I'm not convinced about, from my admittedly very limited experiments, are (a) whether we can actually "erase" it by charging harder/higher, or (b) whether it actually matters in any practical sense.

What

The thing is, my battery should be a poster child for this memory bump at high SOC, if it exists. I basically charge at 0.25C to 92% SOC almost every time, and I do that by switching to CV at 54.2 and holding for 30 minutes. If there were a memory effect that manifests as a capacity fade, I would expect my once-yearly capacity tests to show a meaningful change when I do them. Earlier this year, after about two years of semi-daily use, the capacity fade I observed seemed consistent with the normal degradation we would expect at 250 cycles -- maybe 1.5 or 2%. It does not seem like there is some exaggerated, synthetic loss due to a memory effect developing in the voltage curve.

So, I don't quite know what to make of it. I don't have a battery test lab with the ability to accelerate hundreds or thousands of cycles. I'm skeptical I'll have this battery (or live long enough) long enough to find out. It's a mystery.

This chemistry does seem to exhibit a type of memory effect, at least if we can use that phrase generally to mean a change in the shape of the charge curve.I can see it during my charges at around the point where I tend to float the battery when not in use (in the middle SOC). There is an obvious bump there, in what would otherwise be a pretty perfectly-linear regime:What I'm not convinced about, from my admittedly very limited experiments, are (a) whether we can actually "erase" it by charging harder/higher, or (b) whether it actually matters in any practical sense.What @Luthj is talking about might be the same effect closer to the top of the charge curve. Maybe, there, the voltage rising earlier than expected (at a gradually lower and lower SOC) would fool a naive charging scheme like I use -- a voltage-based one -- into stopping earlier and earlier at lower achieved capacities over time. I've heard a couple of other people talk about this on another forum, but no one actually seems to have much data or hands-on experience with it that they are willing to share.The thing is, my battery should be a poster child for this memory bump at high SOC, if it exists. I basically charge at 0.25C to 92% SOC almost every time, and I do that by switching to CV at 54.2 and holding for 30 minutes. If there were a memory effect that manifests as a capacity fade, I would expect my once-yearly capacity tests to show a meaningful change when I do them. Earlier this year, after about two years of semi-daily use, the capacity fade I observed seemed consistent with the normal degradation we would expect at 250 cycles -- maybe 1.5 or 2%. It does not seem like there is some exaggerated, synthetic loss due to a memory effect developing in the voltage curve.So, I don't quite know what to make of it. I don't have a battery test lab with the ability to accelerate hundreds or thousands of cycles. I'm skeptical I'll have this battery (or live long enough) long enough to find out. It's a mystery.