Xtar VC4S showing low MaH for 18650 batteries.

I was testing some 18650 cheap batteries that came with a headlamp.

They were marked Mixxar and rated (?) 5000ma. I understand this is

way overrated for an 18650. Using this charger I discharged, then

recharged them. This charger showed these batteries fully charged with

~620 and 700 mah !! Wow, like that is real low / bad. They did not hold

up for long in the headlamp either.

I decided to do the same with some new Panasonics which I discharged then

fully charged with ~1100 and ~1200 mah. Terrible. Expecting 2500+ mah.

These are NEW Panasonic NCR18650B.

Now I am wondering about the charger?? Is this considered a good Lithium battery charger??

These charge numbers sure seem low for the Panasonic also.


That’s hard to say but I would suggest testing with a cell that you know has the general rated capacity like a 30Q or a vtc6 and if those numbers look correct then you know its poor batteries.

Yeah all those crappy 5000+mAh batteries are literally crap. You can look up some pictures on BLF/blogs where people opened them and it turns out most often it’s just a tiny cell in a 18650 shell and some cables soldered on, lmao. Them having way under 1000mAh looks pretty normal. It would dispose them, no idea when they will leak or gas in that setup.

As for your Panasonics - do you have other batteries, where you are sure that those are legit to test them against? Where did you buy your Panas? If you got them from ebay or amazon or in a cheapo no-name light, then there is also a good chance those are fakes.

Don’t waste your time, you may damage your charger with that crap.

Agree about the Mixxar cells. It’s quite probably they were that bad.

Re- Testing with the Panasonic. Do you know for a reliable fact they are genuine Panasonic? Fakes exist.
The Xtar has a capacity test function built in. Did you use that?

[The grading function will charge the battery, then discharge it and finally charge it again, it reports the discharged capacity.
The discharge current is fairly moderate at 300mA and it discharges to around 2.65V.]

I purchased them from 18650BatteryStore.com. Checking the receipt, these
cells are / (were) rated for 3400maH.

I have a pair of Orbtronic IMR 26650 5750maH I can try this charger on
for comparison.I had not thought the Panasonic labeled batteries could
be counterfeit also. I did buy the IMR 26650 at orbtronic.com.

The Orbtronic IMR 26650 has fully charged. Charger states 6064 maH, a close
match to the stated 5750 maH! It was in one of my flashlights, and had a voltage
of 3.4V, very discharged.

My charger only takes the voltage down to 3.7V. Somehow I doubt that there
would be that much difference between charging from 3.4V vs 3.7V?

I will be discharge / charge a different set of Panasonics today, purchased earlier.

I don’t find the Xtar VC4S has the command setting to discharge / recharge. Perhaps
other Xtar chargers do. Am I wrong??

Thanks for the help.

Maybe not, but it has a “grading” setting, as @flydiver already wrote before.

3.4v is not ‘very’ discharged depending on the specific battery and age.
Due to the charge/discharge curve of li-on there can be a good deal of capacity from 2.8-3.0v up to 3.4v, and even more between 3.4 > 3.7v.

You might peruse this chart.

Thanks for the responses. It was real interesting to see the discharge curves
for the Panasonic 18650’s. At 3.4V I am only 1/2 discharged! So, these
Panasonic 18650 are really good, I would like to find something where
I can measure the discharge all the way down to 2.8V. Lithium’s do seem
to vary quite a bit depending on the manufacturer.

I really thank you folks, good answers.

I’m having similar issues with ni-mh Ikea Laddas 2450. Erratic capacity figures.

All cells have voltage ‘bounce’ after discharge. It goes back up ‘some amount’ after the current is removed. How much depends on a couple factors, the main ones being; quality+capability of the cell, current used to discharge, and the final voltage level of discharge.
Very low current levels of discharge to say 2.8v, will take a decent cell way down and have modest bounce back to the low 3.xx volt.
High levels of current for discharge will pull it down faster of course, and the bounce back will be higher. For a good cell, it will still be modest. For a crappy cell it will be much higher.

Do NOT assume there is ANY capacity of note left in a cell after discharge based on the bounce voltage. Put it under a load again and it will/should fail to perform very quickly. Try it.

I repeat again, assuming you really do have a Xtar VC4S:
*[The grading function will charge the battery, then discharge it and finally charge it again, it reports the discharged capacity.
The discharge current is fairly moderate at 300mA and it discharges to around 2.65V.]*

300mA is VERY low. A decent AAA NiMh can handle that. 2.65v is low. I stop at 3.0v for discharge. Any li-on cell, even pretty small, that cannot handle 300mA, is a poor cell.
I’m not familiar with that charger personally. Charge current seems to be automatic only and somewhat dependent on the input power capability. This should not much affect li-on except the time it takes, but could well affect NiMh ‘grading’.

If you have not, I suggest you go over the review: Test/review of Charger Xtar VC4S

*Conclusion (from the review)
This charge do not have the usual discharge function, but instead has a “grade” that will charge, discharge and charge battery again to measure capacity and a store that will half charge a battery, it may either charge or discharge the battery to get there. The store function is for LiIon and do not really work for NiMH.
Charging and grading works well for both LiIon and NiMH (The bug is a minor annoyance).*

The cheapie batteries may just be crap cells or even rewrapped used cells, but you'd expect them to have more capacity than that. If the charger is only discharging to 3.7v then that solves that mystery.

Remember that (with "real" cells) the capacity is measured in a certain way. We can think of them as having either "white paper capacity" or "real world working capacity", the latter of which is always a bit less depending on the quality of the cell and the type of use it sees. Generally in lights unless you're running at very low modes all the time, you'll never see full capacity/run time because as current draw/heat goes up, the capacity/voltage goes down from paper specifications.

In the lab, cells are carefully charged and discharged, pretty slowly for almost all of them, in order to measure capacity and other qualities. You can look up your Panasonic batteries' white sheet to see which methods/levels they used if you want to try to replicate that. Usually the cell is discharged down to around 2.7v give or take (some are 2.8 and some go lower) at a low current like 500mA (again, give or take) and may be allowed to rest or may be charged up immediately (capacity test vs cycle life tests). Then it's charged up full normally at 0.2C rate....20% current of the rated capacity, so for example a 2000mAh cell would be charged at 400mA...until it reaches 4.2v. Using these slow rates for discharge helps to reduce heat and also reduce voltage bounce-back, and the slow charge rates reduce heat and give the pixies time to really swell up with joy.

To approximate this yourself without all of the bench testing equipment or a specialized charger that truly gives you some control, you can just drain a cell down low with any flashlight - preferably a "dumb" flashlight that isn't going to shut off at 3v. You can speed it up with a high mode and then change to a low/slow drain mode to finish off. Check the battery a few times with a multimeter to see what voltage it's at (if you don't have a multimeter you could pop it briefly into the charger until it registers a voltage reading, then pull it out and drain some more if needed). In the interest of cell health you can stop at 2.8v even if the white sheet went lower in the lab....and the cell will only be sitting "low" like that very briefly so it isn't going to hurt anything really. Then, select the 0.2C charging rate or as close as you can get to that, charge it up and see what the charger tells you for input capacity. On the cheapie cells since you really have no idea what capacity they have, maybe just guess at 400 or 500 ma and call it good. But doing it this way you'll end up with a much better and at least partially accurate estimation of their capacity.

Note that on white sheets for most cells this low current application is normal, but the sheets will also usually give numbers for a "standard" charge and discharge rate which will be higher...that's just a recommendation for typical use for best performance and perhaps cycle life, but different than how they will test for capacity. Also will see "max" rates which are what the cell may handle (continuously or briefly as a "pulse" such as in turbo modes) without potential damage from heat.

I don't have your charger but it looks like it has some "convenience" features that are useful but it's not really what you'd call an analyzer/tester. But we can still do things the old fashioned way with just a little labor and attention and coming as close as we can to official methods.