Did I Ruin My Battery?

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Oct 5, 2022
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I'm trying to figure out if I have a faulty battery. I've used it recreationally for 2 years now. It's probably been charged under 30 times.

It's a 52V 17.5aH which I purchased new as part of a Bafang mid-drive kit from Johnny Nerdout. I use an eggrider display. I live in upstate New York, and I usually don't ride between the end of Nov and then some time in March or April depending on snow and other weather factors.

During the winter of 2023 to 2024, I built a variable battery charger using off the shelf components which have been identified to be reliable non destructive, UL approved pieces. The components are within my battery's / BMS charge design specs. I used the Meanwell HLG LED power supply.

Once the new charger was built I wanted to put it though it's paces to test it's ability to charge to 80%. I calibrated it's voltage and current outputs using a Fluke 87 V multimeter which I use at work in the telecommunications industry. I used a cheaper ammeter, but that is not as important because the power supply's max output is 175W. I didn't have any mistakes in making the device as far as reversed polarity causing shorts or any kind of arcing from dramatic difference in voltage. I have made literally thousands of electrical branch circuits and battery connections to DC power plants in the telecommunications biz.

The charger worked well, and then I decided I wanted to build a portable charger box that I could use to bring with me camping. The idea would be I would have the charger in the box, but it would also have a downtube battery mount in there where I could use my ebike battery to power a light or charge my phone from the discharge side of the battery.

The homemade battery charger system included an in-line display which shows the charge voltage/ current etc etc. The display is automatically powered up when you plug it into the battery's charge port. When plugged into the battery but not charging it stays lit up and shows the batt voltage

So, I had this 80% charged state battery which I wanted to discharge a bit so I could do a few more tests with adjusting the voltage/current setpoints. While I waited for my downtube battery tray and DC light bulb to come in the mail, I allowed the digital meter which was connected between to the homemade charger and the charge port of my battery to remain plugged into my battery so it could drain it while I waited.

I think this is where I may have gone wrong.


I finished by camp charger single line design and built the basic system outside of the box for testing. I connected the discharge side of the battery to a 52v to 12 v buck converter, and then connected my DC light bulb to the output of the converter. Everything looked to be going well.

At that point I was just waiting for the weather to warm up so I could ride and camp. The season arrived, and I wanted to go for a nice long spring ride. I plugged my bike's factory charger in to top off the battery the night before my ride. When I got to the trail my batt voltage had already dropped from 58.8v to 58.1 overnight. It was always 100% before. During the ride, the discharge seemed normal. I was just starting off with less gas in the tank.

My battery has always been questionable to me because it seemed to reach the Low V cutoff to early in my ride. However I don't have enough life experience with ebikes to know if what is happening is normal. Once the batt voltage gets to 50.1v- 50.0v, it is only a matter of time.

I'm 210 lbs and even on flat terrain on any of my higher PAS setting which would allow my bike to travel say... 12 mph or more on throttle only; I"ll likley touch the Low V cutoff, and my bike shuts down. Sometimes I can pedal though for 10 min or so and start it back up. At that point, if I use a low PAS, I can make it back to the trailhead. Sometimes it won't turn back on. My Low V setting is 43V. I'm not sure if I am being ignorant of the dynamics of voltage sag o. These types of batteries. This Low V cutoff situation has been the case since the battery was brand new.

A couple of questions:

Do any of you start having your Low V setpoints attained when your batt still has like 6-7v before it gets to the Low V setting?

Did leaving the digital meter of my homemade charger connected to the charge port of my battery for a couple if days end up throwing my cell voltages out of whack, so now I can't get them balanced though a standard charge cycle?

Is there a safe way to fix an imbalance such as this?
 
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