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I am looking for a method to test lithium ion batteries that are in a block package.

Think camera rechargeable battery packs that no longer hold their rated runtime. A rated 10 hour battery, only giving 30 minutes of runtime.

A great circuit to built, would be one that can determine the batteries life health. For example, a perfect battery being 100% healthy, while a bad one having a 75% battery health in which I will know to dispose.

I’ve seen some modules online, but I am uncertain if they are compatible/work. & the method of charging/discharging can take around 5 hours of testing per battery cell.

I plan to test 100+ batteries, and 5 hours per battery is timely, so I’m hoping there is another method.

Battery specifics: 3.7V, 1900ma

Test: Good and bad batteries both charge to 4.10V. After letting them sit for 4 days, most drop to 4.09V. Maybe I have to wait 2 weeks to see if they drop 1v?

Test: Testing the batteries internal resistance. I can see that the higher the internal resistance, the more degraded the battery is. This method appears to be the fastest method. Although I haven’t pin pointed if there is a direct relationship for a specific internal resistance to have a specific runtime.

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  • \$\begingroup\$ khrissicks - Hi, This might sound strange, but it seems that you have already identified which batteries give the runtime of 3 hours - because you find that they only give that runtime! So can you edit the question to explain more about exactly what you want, and why doing the procedure you are currently doing isn't good enough? That will help you to get answers which address what you want specifically. Thanks. (Also, as you are new here and Stack Exchange rules are different to typical forums, please see the main site rules & etiquette explained in the tour & help center.) \$\endgroup\$
    – SamGibson ♦
    Commented May 8, 2023 at 22:02
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    \$\begingroup\$ You've either mistyped or wrongly charged your batteries. A full charge of a 1-cell Li-ion is 4.2V. 3.1V is dangerously discharged. \$\endgroup\$
    – LordTeddy
    Commented May 8, 2023 at 22:03
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    \$\begingroup\$ @LordTeddy - Hi, I'm so used to seeing 4.1 V that I didn't register that. Well spotted. Hopefully the OP can explain more. \$\endgroup\$
    – SamGibson ♦
    Commented May 8, 2023 at 22:05
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    \$\begingroup\$ You're asking about a readily available consumer product. They make inexpensive battery testers that will fully charge a lithium, discharge it and tell you the watt-hour results. Guys on Youtube who build their own lithium packs use them a lot and own several. They're cheap. youtu.be/tKg-jIrr_JE?t=609 \$\endgroup\$
    – Harper - Reinstate Monica
    Commented May 9, 2023 at 4:38
  • \$\begingroup\$ Sam, the 3.7V, 1900ma, 7.1 watt/hr battery pack goes into an intercom pack. If I place it in the pack, then I can test how long it takes to discharge, therefor knowing the hour differences between batteries. I have about 200 batteries so this method is rather slow. I also own different batteries of different voltages, so the goal is to sort between the good and the bad batteries. Finding an applicable method to apply to different battery sizes for sorting the bad from the good. \$\endgroup\$
    – khrissicks
    Commented May 10, 2023 at 4:58

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A 3.7v rated Li-ion battery mostly have 4.2V max-charge-rating but they may give full charge indicator if voltage i 4.14, 4.18 etc depending upon charger ic you use.

for low battery if your battery has short ckt protection chip (separate ckt connected to batteries to avoid unintentional burning and blasting) this ckt gives voltage from 3.0 -4.2 V

if your battery is not with protection ckt it will give 0V - 4.2V and it will degrade faster, due to overcharge and over discharge.

Steps to check capacity : full charge battery it should show 4.2V or near keep them unconnected for 3-4 days if voltage loss is more than 1 volt its degraded.

degraded batteries discharge very quickly and give low backup, they discharge even if no load is connected.

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