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CT scans of 1k lithium-ion batteries show quality risks in inexpensive cells

(www.lumafield.com)
287 points jonbruner | 3 comments | 24 Sep 25 19:29 UTC | HN request time: 0.404s | source
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Neywiny ◴[24 Sep 25 22:58 UTC] No.45366921[source]▶
I find their table of advertised vs actual capacity to be misleadingly negative. They only discharged to 3v. 2.7 could be viewed as more standard. 2.5 is not unheard of. For example, the vapvell 4000 they said was around 3000. They even have a note that says that isn't a reasonable capacity estimate. And yet they still put the percentage and the number. As if they've falsely advertised. However, if you go to vapcell's graphs on their website, it all tracks. Feels out of scope for the report and shouldn't have been done
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quickthrowman ◴[26 Sep 25 22:02 UTC] No.45391469[source]▶
How do you even drain a 3.7V lithium ion battery below 3.3V? My devices that use 18650s will not let them go below that. Is it 3.3V nominal and the actual voltage is lower, like how they’re 4.2V fully charged?
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avar ◴[27 Sep 25 09:25 UTC] No.45394350[source]▶

    > How do you even drain a 3.7V lithium
    > ion battery below 3.3V?
Connect the + and - terminals with an appropriately sized resistor, it'll drain all the way to 0V.

    > My devices that use 18650s will
    > not let them go below that.
Because you're not using the + and - terminals, you're using the + and - supply of a BMS, which is connected to those terminals. For this sort of testing you need to bypass the BMS, which'll have its own voltage cutoffs.
replies(1): >>45395352 #
1. quickthrowman ◴[27 Sep 25 13:00 UTC] No.45395352[source]▶
I understand you can discharge a battery completely with a resistor, just like any other capacitor. I also know there’s a battery controller in my device.

My actual question should’ve been ‘Do people really use lithium ion batteries in devices without battery managers?’ I absolutely would not.

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2. avar ◴[27 Sep 25 14:54 UTC] No.45396220[source]▶
Neywiny's comment upthread isn't that you should use these without a BMS, but that the review is relatively less useful because it's stopping testing at a relatively high voltage. E.g. if you search for "panasonic_ncr18650b.pdf" you'll find that Panasonic's own datasheets use a cutoff of 2.5v.
3. Liftyee ◴[27 Sep 25 15:05 UTC] No.45396309[source]▶
Some do. Anecdotally, some (uncommon, enthusiast-grade) flashlights I use don't have battery managers/over discharge protection, though most of mine do. If you can bear the responsibility of maintaining and storing the batteries properly, IMO there's no significant problems.