XTAR VC2 not fully charging?!

I've been using the charger for about 4 days now and since day one I have noticed the batteries don't come off the charger reading 4.2V. At first I wrote it off as maybe my voltmeter was off, but I have had a chance to run a couple batteries through my other charger and compare run times simultaneously.

My other charger is a cheap one, generic 2 battery charger, and the batteries consistently come off it reading 4.3-4.4V. The XTAR is giving me different results with each battery, some come off as low as 4.13V, while most are 4.14, some get up to 4.17, and ONE battery was at 4.18V. I've noticed the digital voltmeter also usually jumps to 4.2 prematurely. It will say 4.2, and keep charging for several mAH. I ran one battery down to 2.75V to see what the charger would do with it. It said 4.2V within 30 minutes, and continued to charge for about 16 hours loading the remaining 2200 mAH for a total of 2758 mAH in a battery that is supposed to be rated at 2400mAH. When I took it off charge, it only read 4.17 with the voltmeter. I stuck it on my old charger and it continued to charge for 3 hours and came off at 4.23V.

anybody else had similar issues? Is there something wrong with the charger or ...?

Wow , _ U have a serious Problem !

Lets start with one problem at a time ...

Termination voltage .. Termination voltage is variable possibly due to the condition ( internal resistance ) of each battery .. The lower the termination voltage , quite possibly the higher the internal resistance .. If you buy a smart charger , the charger may take notice of the resistance to charging and terminate earlier .. One way to check against this is with an old brute force charger ( Trustfire TR001 = Responsible for a few flame events , but never mind ) ... So if you have one of these older chargers , charge you batteries in that and hope it sort of terminates at 4.2v .. The thing to do is check voltage on removal from charger , then check again about 2 hours latter and see what the resting voltage is and check the variable .. Good batteries may possibly sag as much as 0.01v ( 4.2 - 4.19v ) or not at all .. ( Not at all = Very good )

Other charger :

Consistently charged to 4.3 / 4.4v , .......................... Holly smoke batman !

Eeeeeeer , that's .................................. BAD ! And over time would stress the batteries and quite possibly increase the speed of degradation by some margin .

4.2v Prematurely :

Ok , Im not there to see for myself , but at a certain point the charger will indicate 4.2v .. The gauge is somewhat coarse , so ???? ( Not the end of the world )

And yes it may indicate this for quite some time , especially with larger batteries ....

Current in VS current out :

Yes , usually ( like 100% of the time ) more energy goes into charging a battery than discharging a battery ... ( Physics )

There is a certain amount of Variable loss in charging ( energy ) so to put 2600mA into a 2600mAh battery may take 2900mA or more depending on those nasty variables .

Your first cheap charger is unsafe. Your new one is doing it right.
You can look this stuff up: li-ion cell overcharge - Google Search
finds, for example, this:

(Emphasis added)

Read through slowly and carefully, with attention to the diagrams, this may help:
http://lygte-info.dk/review/Review%20Charger%20Xtar%20VC2%20UK.html

And on this page
http://lygte-info.dk/info/How%20do%20I%20test%20a%20charger%20UK.html
Look at the diagram labeled

Look back at that first link, the last bit I boldfaced.
That bit about becoming hazardous — know what lithium plating out means?
You can look it up: li-ion plating out lithium - Google Search

As the guy says in the movie: Do you feel lucky? Well, do ya?

Don’t forget — this stuff isn’t consumer-grade technology, lithium-ion cells are definitely not ready for prime time.
The chemistry isn’t fully understood — the problem of metallic lithium plating out from overcharging, for example, is still news right now:

I was about to say welcome to my world, none of the chargers i have bought so far can get to 4.2V but your setup sounds crazy all around.

Your batteries are probably toast if you've been charging them to 4.3-4.4V. Cells that are damaged will have higher internal resistance, and will take much longer to terminate once in constant voltage mode. The total mAh means that's how much energy was put into the battery, but the battery's internal resistance will eat the rest of the energy. So if a 2200mAh battery is takes 2758mAh worth of energy it probably has a lot of internal resistance.

Most of the energy is put into the battery in the constant current phase (70%-80%), then the constant voltage phase tops them off at a much slower rate. That is how it is supposed to work, but if your cell has a lot of internal resistance (damaged) it will have a hard time getting to the constant voltage termination point.

If a battery charged at 16 hours after hitting 4.2v, that battery is toast. Period.

I'm really sorry I typo'd and meant that my old charger consistently charged to 4.23/4.24V not 4.3-4.4.

The batteries do drop a little voltage over a 12 hour period, usually not more than .02V.

I would almost think it could be bad batteries, but I have 4 different types of 18650's, some from a laptop battery pack FS thread here, in which another member bought some, charged and checked them, and was reselling as good batteries. I can't believe the batteries are at fault if he was getting some from the same lot to charge to full capacity and stay that way.

If a battery charged at 16 hours after hitting 4.2v, that battery is toast. Period.


The VC2 charger said it was @ 4.2V, when I pulledif off after the charger said it was fully charged my voltmeter said it was @ 4.17V, I put it on my old charger, charged for about 3 hours and my voltmeter read 4.23V.

Termination voltage will vary. Exactly 4.20v is never guaranteed.

Do note that li-ions are suppose to spend some time time charging at 4.2 (or whatever the termination voltage is). That is the constant voltage (cv) phase. Old, worn, damaged batteries can spend longer in cv phase.

When the green line starts dropping that is the cv phase. You can see the old 16340 IMR spends most of its time in the cv.

This battery sounds old or damaged.

How good is your DMM? When was it last calibrated? What amb temp are you working at?

I don’t want you to answer the above questions, just trying to point out that there are so many things that can effect a Voltage reading.

I'm getting the hint that you guys are pointing out CV charge phase is done at 4.2V, what I don't understand is why a fresh off the charger battery only reads 4.13-4.17V with my voltmeter.

There is about a 20 minute difference in runtimes with using (the same Sanyo 2600mAH battery) my old charger vs using the VC2. If my oLD charger is slightly overcharging the batteries (IF that's the case..?) I'll buy another cheap charger that will hopefully overcharge them the same (up to 4.24V) and use it instead. I don't care about the degradation of the battery, if it explodes or catches on fire. It's never anywhere that will do any damage except my hand while its in the flashlight, and I have over 100 batteries I can burn through. I charge the batteries at work, plugged into a GFCI surge strip plugged into a GFCI outlet ran off a 20A breaker bolted to a steel wall with no paint in a room made of 1/4"-1/8" steel.........on a barge in the middle of the river! Literally I don't think it could be much safer an environment for charging a battery, let it burn!

i had to let one of my flashlights run for about 26 hours to get the battery discharged to that point, used it since it does as good as the rest. I have a bunch but I've only been messing with about a dozen the last week or so.

As soon as a charger ends the voltage can drop, particularly with worn batteries. Look at the voltage line on the charts I posted. It drops right at the end of charge (yellow vertical line). When you overcharge, as your old charger does, it can drop less or mask the drop.

4.17v is perfectly fine. Again, exactly 4.20 is not guaranteed by any chargers specs. Much better 0.03v under than over.

gotcha :)

Just to make sure: you know not to inhale, and why, and for how long, when your toast finally catches on fire?