I got a new Vapcell BL4 charger, and I’ve been using it to test some batteries I have. In the test mode it does a full charge, then a full drain (and eventually a full charge, although I take the battery out to charge it in another charger for comparison).
The numbers I’m getting are weird. It seems like it consistently over-reports capacity. It charges to 4.20v, then drains to 2.55v. but the numbers are get are almost consistently higher than manufacturer stated capacity, but what’s even worse, when I put it into a LiitoKala charger (not a fancy one with testing, just a plain charger), it charges less than what’s supposedly was drained, so either it stops earlier (though it gets to 4.20v too), or something else is off.
Some examples:
Wurkkos 21700 5000mah - Tested at 5200, Recharge to Full - 4830
Vapcell 18350 F16 1600mah - Tested at 1720 (showed 1650 at 2.8v), Recharged to Full - 1550
Sofirn 18350 1100mah - Tested at 1300 (!), Recharged to Full - 1150
LiitoKala King 21700 6000mah - Tested at 6650 (showed 6300 at 2.8v)
Vapcell 18650 F38 3800mah - Tested at 4270
(I didn’t pull out the last two on time to measure their recharge unfortunately)
Yes this potentially appears to be the case - it appears you are getting readings 5-18% higher than the rated capacity.
As an aside, do note that capacity ratings are related to discharge current, at low currents it would be normal to get slightly over rated capacity while higher currents than used for the factory test will result in lower capacity.
Not sure there is anything particularly weird with your unit, I think accuracy of these inexpensive electronic devices is down to luck- unless the manufacturers start using high precision components then I would expect variation to be normal between individual units. That said, your numbers do seem a little inconsistent, if it always read 10% over it would be easy to subtract 10% to get a better idea of the true capacity.
I guess what you’re really asking is: “is it faulty?”. In your shoes, I’d be a slightly annoyed the capacity is so over-stated but could live with it given the other benefits this charger offers (USB C input, Etc). If someone requires highly accurate capacity measurements, I would understand if they considered this charger faulty, however, I’m yet to see a charger that actually advertises accuracy of capacity test, so in a sense, it’s within specifications (i.e, none).
For accurate capacity tests I’d likely go with an electronic load type set-up rather than an “all in one, multi-chemistry charger”.
One last point, the Liitokala charger seems to under-state the mAh fed to the cell, dueing charging, it is normal to lose energy due to heat so I would expect values c.5%(?) higher than actual capacity.
Assuming I use this to compare batteries I purchase, and to test health of batteries I own over time, is it fair to assume that while it over reports, it will be more or less consistent in over reporting? so the relative numbers will make sense? or is it too presumptuous.
Are there other charger/testers of this genre that are more recommended? i.e. more accurate? ideally still with USBC input as this is the most convenient/flexible?
Good questions, I would assume the over-reporting would be mostly consistent, however I forgot to ask a pertinent question - were all these tests performed in the same charger slot?
I’ve an older charger (Zanflare C4) from when they were a popular reccomendation- 3 of the 4 slots report similarly dubious internal resistance values but one slot (maybe slot 3? I’d have to check) is always completely random. I wonder if the BL4 also has between-slot inconsistency for the capacity test.
With regards to other gear, I’ve (literally) just ordered a DL24 electronic load and a ZB2L3 module along with some USB C meters to do some capacity testing of cells/batteries/powerbanks myself. These seem fairly well regarded, I’m not sure what else exists for “quality” capacity testing at a hobby level.
None of the above options are as easy as “plug in usb c power supply, insert battery, press button” though.
My BL4 over charges my 21700 batteries to 4.23 and 4.22 volts. Confirmed using a multimeter and Finirsi HRM10. I haven’t tried capacity testing since I don’t like overcharging cells. I emailed Vapcell and Flashlightgo and never received an answer from Vapcell. Flashlightgo was emailing me back but did not have an answer. I only use it for smaller cells now, since it slightly undercharges them. The BL4 doesn’t seem to be very accurate. I have an Xtar charger that consistently charges all my cells to 4.2. The BL4 over and under charges.
Well - what I’m taking from this discussion is that all these Chinese manufacturers have tolerances that go beyond our OCD
I just checked 4 different charges I have with my volt meter (which may be Chinese too ;-))
The Vapcell BL4, The XTAR MX4, and the LiitoKala Lii-S8 - All get my 21700s out at 4.185
I have another LiitoKala - Lii-PD4 - This, for some unexplainable reason, gets them out at 4.21-4.215. Slightly overcharge, but I think reasonably so within tolerance.
I also measured a 21700 that was fully drained by my Vapcell BL4 - it was at 2.70 by my voltmeter, despite the BL4 claiming it was at 2.55. so it’s not an “offset”, cause at the high end the BL4 claims higher (4.2 vs measured 4.185) and at the low end it claims lower (2.55 vs measured 2.7) - so overall I think everything is not extremely accurate.
At the same time, given that the battery is acually working within range in the charge/drain test (4.185–>2.70) then the higher capacity readout seems like highly inaccurate and way more outside of reasonable tolerances. but - it is what it is. I may get an XTAR VX4 at some point, but Im not sure I want to spend more money on this rabbit hole I got into lately
Interestingly, when I test the IKEA Ladda AAA that I just bought with March 2025 batches, it was under report a bit, my S4+ reported higher to around 760 to 800. So BL4 seems to do cap test Ni-MH differently
This is mostly likely because voltage sags when discharging, and will take a little bit of time to recover after discharge ceases. This recovery will be in progress in the time between when discharge completes, and when you remove the battery to measure with your multimeter. Likewise when charging - voltage will be slightly elevated, and then drop to the rest voltage after charging ceases.
From TimMc’s review of this charger, see this specific graph for a very good example of voltage rebound while discharging (red line). It terminates around 2.55V. About 10 minutes later, the voltage is back up to near 2.8V, and a few hours later, it is at 2.9V. To be clear, this is a behavior of the battery, not the charger, and different batteries will show more or less of an effect.
