I have bought a headlamp for serveral months
Its lighting duration was getting shorter and shorter, so I took a look at the battery by taking it apart. I found that there is no capacity label on it.
I decide to test the battery capacity. Wait for my news
It’s nice of you to join us, AIssea!
I’m guessing that AI does not stand for Artificial Intelligence because you’re a real person. 
Thank you so much.I am a new member in this forum.
There is a simple USB passthrough dongle called ‘KEWEISI USB Tester’ or something similar. On sale you can have it for $2. I use it to connect to a battery charger every time I charge a battery. It will measure mAh passed through it. As long as the charger doesn’t do anything smart, it will give me an estimate of the battery capacity. I keep my eye on batteries for every charge so I can pick out the failing ones as soon as possible to avoid a disaster.
Good advice. I will consider buying one.
Hi and welcome. I am confused a bit. Do you have the tester that is pictured in your post above?
If so, I am not sure what else you would need to test the cell capacity.
The cheap passthrough USB devices mentioned would not be as accurate (likely) and charging numbers are not as good for measuring capacity.
If you do get one of those, make sure it has the connectors that you need and that it supports the charging protocols that you will use. I would be surprised if something like was mentioned above would do either.
here is the test result!
I charge the battery fully and discharge to 3V(Discharge cut-off voltage should be 3.2v）.
the capacity of battery is 3.1ah,which is 3100mah.
1 Thank
Nicely done, good test.
How do you like that battery tester you have there? The specs look amazing. If it’s accurate that’s a great device for single cell testing. I want one.
-Charge and discharge, 0.5A-50A, 5V max.
-Kelvin connection
-Graphing software
Ooooo…$200 shipped…hmm. Thats not totally unreasonable though if those specs are right.
Where’d you get it?
BTW, the capacity was written on that battery eh? I can see it in the picture lol
Might as well double check though
The capacity wasn’t written on the battery. That’s why I want to test.
I bought the tester on alibaba. It’s YPSDZ-0550.Maybe you can go and find it
Ya it is. If you know where to look. Here, I’ll help you find it.
It’s an Eve 35V. Eve labels their cells by rated capacity. 35 = 3500mAh. You can also pull the datasheet to double check. Here found that for you too.
1 Thank
Thanks for you sharing!
I test out the true capacity is 3100mAh.Has the battery performance decreased？
Of course, the battery performance is always decreasing as it ages. Every cycle you lose a tiny bit more.
It’s probably a little better than the test suggest though. They use the industry standard 0.2C discharge, and a 2.5V cutoff. Those two alone would’ve got you an extra 100mAh probably
1 Thank
Maybe this will help It is for the EVE 35V. Many cells will show a discharge to 2.5 volts and discharge termination at or below 0.1 amps.
This would give a bit more indicated capacity than terminating at 3.0V. Even at that, I am happy when I get capacity measured at 90% of the labeled or claimed capacity. So if you tested with the same parameters that they used and your meter it accurate something like 3150 -3200 mAh on a new 35V cell is not bad. Bottom line is that that cell is not measuring bad for a used cell.
I should have read your post first…
From the data sheet
Discharge: CC 0.2C/0.33C/0.5C/1C/2C/3C to 2.5V
OK, but I would avoid the ~$4 ones. You like good equipment based on the tester you have. Get something decent.
These are pretty good. I have a couple. The Blue Tooth app is nice.
https://www.amazon.com/RD-Bluetooth-Trigger-Digital-Display/dp/B09B1YKYVG
Or for more money, you get a bigger display and cover just about every protocol:
https://www.amazon.com/Digital-Voltmeter-Current-Protocol-Detection/dp/B0BMQ9ZQZK
I also have one of these and like it. I believe both allow firmware upgrades.
You can do capacity testing to if you have something to dump the power into.