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Hi I've have a couple of batteries of these two types, some of them are below 2,5V making me unable to make a CAP test on them, whenever I try my Foxnovo 4-Slots Intelligent Battery Charger beeps four times and "seems, not sure" to remove some voltage from the battery?

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The one with the purple top has "A NJGA59 034688" written on it. The one with the orange top has "C IEOFJT4 077773" written on it.

They come from a semi-old dell laptop battery, from Toshiba and Sanyo I believe.

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  • \$\begingroup\$ Have you googled about letting the voltage on a Li-ion battery drop below 2.7 volts and what you should expect in terms of them being serviceable? If not, why not? \$\endgroup\$
    – Andy aka
    Commented Aug 5, 2017 at 18:20
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    \$\begingroup\$ I don't know what kind of cells those are. But you can try to trickle charge them up above 2.5V. Use a current limited bench supply (maybe 100 mA or so). Or you can use a resistor to limit the current to something under 100 mA. You can try this for around 30 minutes or so. If the voltage does not come up, the cell is probably beyond hope. The usual rules apply. Under no circumstances should you let them charge above 4.2V, nor should you float them at 4.2V after they are fully charged. \$\endgroup\$
    – user57037
    Commented Aug 5, 2017 at 18:21
  • \$\begingroup\$ The idea of the trickle charge is just to get the cell voltage up to a point where the foxnovo will try to charge them. \$\endgroup\$
    – user57037
    Commented Aug 5, 2017 at 18:22
  • \$\begingroup\$ electronics.stackexchange.com/questions/219222/… \$\endgroup\$
    – Andy aka
    Commented Aug 5, 2017 at 18:24
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    \$\begingroup\$ Thank you very much guys, you're all been a big help! Sad to hear that no one recognize these batteries yet. I'll try tickle charge them, would using the foxnovo charger and just pull the battery back and releasing it tickle charge them? \$\endgroup\$
    – Athax
    Commented Aug 5, 2017 at 18:40

2 Answers 2

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These are the classic 18650-type OEM batteries, Li-ion chemistry, charge voltage should be 4.2 V. Their design capacity might be 2500 - 3000 mAh, depending how long ago the were made.

If some are "undervoltaged", below 3.0 V (or even to zero), you can try to recover them by applying "pre-charge" current, 100 - 200 mA, until they get to 3.3V-something, then a normal charger will work. Be aware however that the battery capacity might be substantially reduced, down to 20 - 40%, or it could remain dead.

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  • \$\begingroup\$ Thank you but I've read so many scare stories by now about reanimating the batteries. I'm just considering getting rid of them. I've tried charging two of them with 0.50a that had 3.6v but they got really hot around 60C. So I just stopped it and trew them to the battery bin. \$\endgroup\$
    – Athax
    Commented Aug 6, 2017 at 15:39
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    \$\begingroup\$ @Athax, Why 500 mA? Dodn't you listen to advices here? 500 mA is too much for pre-charge of dead/overdischarged batteries. With 500 mA and 60C overheat, you came too close to being another example of a scare story. \$\endgroup\$
    – Ale..chenski
    Commented Aug 6, 2017 at 16:42
  • \$\begingroup\$ Oh no these wasn't dead batteries, there was two in the pack that had over 3.6 voltage and would be recognized by my foxnovo. \$\endgroup\$
    – Athax
    Commented Aug 8, 2017 at 9:34
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This is what worked for me when I had couple of unprotected Li-ion batteries in the past. I don't know if it's a good procedure but had heard from somewhere that this was safe.

  • The main purpose I was doing this because 4.2 V chargers were unable to detect these batteries once they go beyond 3.1 V

  • I had an Arduino Uno board which had 3.3 V power pin which can hardly provide around 50 mA power.

  • I used to connect individual battery cells to 3.3 V through a series resistor of 100 ohms (1/2 or 1 W) & GND pins for 10-15 mins to trickle charge them.

  • Battery voltage was raised upto around 3.2 V by this technique.

  • Later they were removed & connected to 4.2 charging circuit which used to detect the batteries.

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  • \$\begingroup\$ I'll consider doing this as I have an Arduino Nano! Thx for it, does this work for batteries all the way down to 1v? \$\endgroup\$
    – Athax
    Commented Aug 5, 2017 at 19:29
  • \$\begingroup\$ NOT recommended. But it should be OK if you put a resistor in series between 3.3V and the battery. Maybe about a 33 or 47 Ohm resistor. The resistor may get a bit hot. If the battery gets hot at all, remove it. If it doesn't get hot, you should be able to leave it for up to an hour or so. If the voltage does not come up and stay up after an hour, the battery is probably not recoverable. \$\endgroup\$
    – user57037
    Commented Aug 6, 2017 at 0:11
  • \$\begingroup\$ @Athax yes even zero voltage Li-ion battery I had trickled charged. And I think it's safe as Arduino Uno board's 3.3 V source is capable of only 50 mA current. You check the current rating of 3.3 V voltage regulator of Arduino Nano from its datasheet before proceeding. \$\endgroup\$
    – Nihal
    Commented Aug 6, 2017 at 1:09
  • \$\begingroup\$ @Nihal, when a regulator says 3.3V 50mA, that usually means it can supply at least 50mA. It may supply quite a bit more. Typical regulators do not have precision current limits like a good bench supply. So if you directly connect a 3.3V regulator to a discharged cell, you really don't know what the current will be. This is why I recommend the resistor between cell and regulator. \$\endgroup\$
    – user57037
    Commented Aug 6, 2017 at 17:56
  • \$\begingroup\$ @mkeith Yes it's better to use a resistor in series with the battery. I found this procedure back in my school days and I didn't use any resistor that time & both battery & Arduino's regulator were working normally as expected even after undergoing such a process. I have updated my answer as per your suggestion. \$\endgroup\$
    – Nihal
    Commented Aug 6, 2017 at 18:14

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