voltage recovery

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Reading voltage from a freshly used battery will be a lower bound for a battery's steady state voltage...that is well known in battery circles.  I was curious to see how much and how fast voltage would naturally recover following use.  Therefore, I started logging voltage and time after use following my last lawn mow.  I expected steady state to be achieved in an hour or so and only gain 1V at max.  After all, my ebike batteries recover to steady state in that time frame...why would eGo batteries be any different?

Well, my eGo battery *is* quite different.  It's been over 10 days and I'm STILL seeing incremental increases in voltage.  Hot off the lawn mower 10 days ago, the voltage was 43.03V.  Now it's 46.18V and continuing to increase!  This defies my understanding.  Can anyone help me explain this?

For comparison, my ebike battery hot off my last long and hard bike ride, the voltage was 46.53V.  An hour and 15 minutes later, it achieved its steady state voltage of 46.74V.  Not even a quarter of a volt in about an hour!  The eGo battery has gained over 3V and has yet to reach steady state in 10 days!!!  What in the world is going on in there?
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Nick can't be blank

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Posted 3 weeks ago

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Blue Angel, Champion

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Probably has to do with the power draw and cell temperature. I’m guessing, but the more power drawn and the higher the temp, the more recovery after rest.

If you deplete a battery in the mower, you can put it on a blower and it will work fine for a while on low power. The higher power draw of the mower means higher voltage drop in use (under load).
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Prairiedog

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I am curious why this matters? Anyway, if you are reading it on the charger, the battery continues to trickle charge for 30 days, then reduces charge by 30% for long term storage. maybe you are picking up on that. I thought it had to do with better batteries moderating voltage recovery to improve battery life. Fast, unmodulated recovery means more stress on the cells and they wear out faster. Part of why Ego is great is their circuitry is supposed to manage rapid recovery for quick recharges while maximizing batt life. Does the thing work as you expect it to? If so, then you probably don't need to be concerned about it.
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Nick can't be blank

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It's not a matter of cell temperature.  After a couple hours, the temperature steadies.  It's been days.

It matters because it's odd to see batteries continue to gain voltage when they are sitting idle, not connected to a charger.

btw, the unused, uncharged battery sitting in a controlled environment is now at 46.38V, which is more than it was when I first started this post a week ago.  None of my other batteries exhibit this "continually increase voltage" phenomenon.  I find that extremely weird.  It's okay if you don't.  And it's also okay to say you don't know why this happens.
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Bryan

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Given that there is a lot of circuitry involved to protect the battery pack from extreme temperature, overdischarge, and over-charge...I suppose what you're really asking is if the voltage readings you're seeing is intended by design or not and why? I don't know the answer but hopefully someone that knows will see your post. I'm curious now too.
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Oregon Mike, Champion

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I've worked, years ago, with extremely high voltage capacitors, in the thousands of volts and tens to hundreds of farads, and they always had to have a shorting bar installed across them. Just sitting on the shelf they would develop a charge if they weren't constantly shorted. I also don't know the reason why, but as capacitors are also a form of energy storage device, perhaps there is some similarity in how they might "pick up" a charge from out of the air?
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Bryan

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Wireless charging, Mike! Now that would be a great idea.
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Oregon Mike, Champion

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Yeah, Bryan, not a clue why it happens but it does. Just wild.