Married cells uneven charge. Strange charger behaviour

Yes, as the title shows: I have some married couples and triples who are purchased together, charged together and used together. When I put them in for recharge all can show 3,7V at the screen. Still, when one or two of them are fully charged at 4,2V one can still be at 3,9V. It will reach 4,2V but it can take another hour.

Other cases: the charger can show fully charged despite the voltage is only 4,0V. When I move the cell to another slot it continues to charge, though. Or one of the cell will never reach fully charged status but the display shows 4,2V. When I move the cell to another slot it soon shows fully charged. This occurs now and then with my Fenix ARE-C2 charger.

These issues makes me not to trust either the batteries or the charger. Are these things normal?...
I apologize if these questions are answered somewhere in some thread but I couldnt find it.

Have you marked the cells to see if the same one is coming in second or stopping short (perhaps writing a #1 and #2 on the cells/labels)? If it's the same cell every time, regardless of which slot you put that cell in, it's the cell. Otherwise, it could be the charger. Other things to try include measuring internal resistance of each cell.

Either way, though...honestly, at this point, I would probably relegate both cells to single-cell lights only (or replace them). But do ensure it's not the charger first. If one always charges slower in slot #2 for instance, regardless of which cell, it could just be the charger.

Thinking it is the charger. Are you using a decent multimeter to check volts? Do you have another meter to corroborate? What brand and how old are the batteries?
Hope you get it sorted out.

KentuckyMike said:

Have you marked the cells to see if the same one is coming in second or stopping short (perhaps writing a #1 and #2 on the cells/labels)? If it's the same cell every time, regardless of which slot you put that cell in, it's the cell. Otherwise, it could be the charger. Other things to try include measuring internal resistance of each cell.

Either way, though...honestly, at this point, I would probably relegate both cells to single-cell lights only (or replace them). But do ensure it's not the charger first. If one always charges slower in slot #2 for instance, regardless of which cell, it could just be the charger.

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I have marked some of the married cells with individual labels but not all. I will do a more careful check next time.

KITROBASKIN said:

Thinking it is the charger. Are you using a decent multimeter to check volts? Do you have another meter to corroborate? What brand and how old are the batteries?
Hope you get it sorted out.

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No, I have no multimeter, only chargers. The batteries are several years old but have not been cycled more than a dozens of times each and are only brand quality models: Eagletac, Keeppower, AW and so on. I have not noted specifically which cells or brands are included in the issue otherwise than the last tripple were Eagtac 3400mAh.


I have several Li-Ion chargers: the first I got was Pila IBC, then Fenix ARE-C2, Keeppower L2. I think it once was some strange thing with the Keeppower charger as well but I don't remember exactly. I ordered an Xtar VP4 Plus Dragon charger and will receive it any day.

I very much suspect that the Fenix charger has some issue because it's enough to move the cell to another slot to get different result. There may be som issue with some of the cells too.
Henceforth I will do a more careful investigation of which cells differ from the other and maybe get a multimeter as well.

Thank you both for replies and advices!

Swedpat said:

Yes, as the title shows: I have some married couples and triples who are purchased together, charged together and used together. When I put them in for recharge all can show 3,7V at the screen. Still, when one or two of them are fully charged at 4,2V one can still be at 3,9V. It will reach 4,2V but it can take another hour [...]

Click to expand...

They may not be from the same batch, so manufacturing tolerances could be large. Also, even if they were used together, one cell may have been exposed to more heat than another, so it will age/degrade more quickly (this is why we often see laptop cells with one or two very bad cells and the others still good). In particular, one of the married cells may have much higher IR than the other(s), and this will slow down its charge. Did you test the IR on the cells? Also you should permute them in the charger slots to rule out charger slot-variations

Gauss163 said:

They may not be from the same batch, so manufacturing tolerances could be large. Also, even if they were used together, one cell may have been exposed to more heat than another, so it will age/degrade more quickly (this is why we often see laptop cells with one or two very bad cells and the others still good). In particular, one of the married cells may have much higher IR than the other(s), and this will slow down its charge. Did you test the IR on the cells? Also you should permute them in the charger slots to rule out charger slot-variations

Click to expand...

Yes, I understand that even if I order several batteries with the same order they may not be of same production batch.
It's obvious my Fenix charger ARE-C2 does not work very good. Many times it shows fully charged 18650 at 4,1V while another 18650 can be at 4,2V and never show fully charged. But when I change slot the display can show fully charged. An Eneloop can be showed at fully charged at 1,3V but when I move it to another slot it continues to 1,4 or 1,5V(with a single digit on the screen I understand it can be correct both of the values because 1,45 is just on the limit.) I also use a Keeppower L2 charger which uses 2digits but it is slower.
My newest charger is XTAR Dragon VP4 plus. This has the function to measure internal resistance so I will give it a try.

Most likely it was the charger's fault. Now you've got the best charger possible (Xtar chargers are rated very high by HKJ) to settle the issue.