Why did my battery read 0.00v?

Sorry for the dumb questions. I was using my 6P with a M61 on two AW RCR123s and I let the batteries run until it shut off. I used it two times after that for about 5 seconds and it was really dead and no longer turned on. I had had a feeling that the batteries were low and most likely needed to be charged. I normally check the voltage and charge my batteries when they are around 3.8v. I always check the voltage on my batteries that have been drained before I charge them and saw that one battery had 3.32v and the other one read 0.00v on my DMM. I also had put the batteries to charge on my WF-139 and the slot charge indicator light where i put the 0.00v battery turned green like it was fully charged. I wiggled the battery thinking it did not make good contact and finally it went red showing it was charging. The 0.00v came off the charger at 3.16v and the 3.32V battery took like 5 min longer to charge and came out at 3.17v. Also I know you are not supposed to mix batteries with different voltages, but do they have to be exactly the same voltage or what is the voltage gap/difference that would be OK. Like a 4.10v battery and a 3.93v battery is the 0.17 difference too much? Thanks.

when the battery goes to 0.00, that means the protection circuit has tripped to help protect the battery from damage. a drop onto the charger should reset the circuit fine.

can't really answer question 2 as I am not a battery pro.

csshih said:

when the battery goes to 0.00, that means the protection circuit has tripped to help protect the battery from damage. a drop onto the charger should reset the circuit fine.

can't really answer question 2 as I am not a battery pro.

Click to expand...

If the charger does not re-set it ..

get a ?? [ What have you got ? ] 18650 and put [ from the good cell ] neg to neg and Positive to positive , and this will hopefully trip the protection circuit and you can charge the battery . A few seconds should be enough , it may take a few tries .

I recently overdischarged a battery a bit and set off the overdischarge circuit. The charger wouldn't charge the battery so I bypassed the protection circuit at the negative end of the battery and charged the battery directly. Once the battery's voltage went above something like 2.5V, the protection circuit allowed the battery to be charged normally again.

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If you don't know the answer to that question ..........


You also don't know why you should not let it do that.

Don't start a habit of doing that on multi-cell lights. Until you understand battery hazards .

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Sorry for the dumb questions. I was using my 6P with a M61 on two AW RCR123s and I let the batteries run until it shut off. I used it two times after that for about 5 seconds and it was really dead and no longer turned on. I had had a feeling that the batteries were low and most likely needed to be charged. I normally check the voltage and charge my batteries when they are around 3.8v. I always check the voltage on my batteries that have been drained before I charge them and saw that one battery had 3.32v and the other one read 0.00v on my DMM.
Nothing wrong with your practices. IMHO its a good practice to measure RCR123 voltage on a good meter.


I also had put the batteries to charge on my WF-139 and the slot charge indicator light where i put the 0.00v battery turned green like it was fully charged.
Yes the WF-139 (green-flashing version) will not attempt to charge any cell that is less than ~2.75V. I have two WF-139s, purchased from DX about 18 months apart from each other. Both are the green flashing versions and they both behave the same way. The light automatically turns green, an terminates the charge (or never begins in the first place) if cell voltage is less than ~2.75

I wiggled the battery thinking it did not make good contact and finally it went red showing it was charging. The 0.00v came off the charger at 3.16v and the 3.32V battery took like 5 min longer to charge and came out at 3.17v.
Something strange is going on. That WF-139 (if its like either of my chargers) should not have begun to charge a cell that measures 0V. Furthermore, it should have fully charged the cells to ~4.15-4.2. I have never measured a healthy cell at ~3.16 fresh out of the WF-139.

Also I know you are not supposed to mix batteries with different voltages, but do they have to be exactly the same voltage or what is the voltage gap/difference that would be OK. Like a 4.10v battery and a 3.93v battery is the 0.17 difference too much? Thanks.
IMHO .17V difference is too much.... especially with a high-C or incan application. My 16340 cells measure ~4.16 fresh off my chargers. After about 4-5 weeks they measure ~4.16 - 4.14V. I'll re-top them off and use them immediately. Although I have used 4.16~4.14 together in lower current LED lights without topping off, with no ill-effects. But then again I am careful not to over-discharge the cells. With my 2-cell incans (A2 and M2) I ALWAYS (!!) top off my cells and make sure the cells are at their peak.

You should also be aware that the WF-139 has shown some strange behavior when used with protected cells.

I have the green blinky version and the non blinky version of the WF-139. Having tripped protection a couple of times, I can say that the WF-139 doesn't automatically charge a dead cell, but I have witnessed the protection resetting twice now... Both times wiggling the cell. The 139 has an open circuit voltage of 4.2V when nothing is in the bay, and nothing is charging... maybe the wiggling connects and disconnects the battery a couple of times... and i dunno... resets protection just like shorting the battery would do.

My guess is that the very short bursts of 4.2v seems to kick it over enough to start the charge

Thanks for the replies and info. Sorry for the typo I meant to say that the batteries where 4.16 and 4.17v off my charger. I will discountinue use of my light as soon as the over-discharging protection kicks in (light shuts off the first time). I was at work and wanted to squezze out a little more light to check something. I just got a bored 6P from Oveready and will start using 18650s and just use my RCR123s on my single cell lights. I would still want to know the safe voltage difference I can use two batteries with different voltage. I used the two RCRs with the .17v difference and it worked fine but discountined use and just put the batteries in my single cell lights. I have noticed the two batteries also dont drain/discharge the same I have taken the batteries out and have seen a gap in voltage difference, so voltages are going to differ as one uses the flashlight at some point regardless if both batteries had the same voltage when off they came off the charger and put in flashlight.

I recently bought 4 18500s from a reputable vendor, reputable brand. Ran the first 2 down ~1/2 way based on posted values (no I did not measure voltage). Charged in Pila IBC charger, put back in light. Only came on very dim the next day.

THEN I measured voltage (lesson learned - I had got lazy about this) - one was at 0.00v. Vendor sent me new 18500 & 0v one is going back. Lesson learned. 1000 lumen drop in is fun, but I keep batteries in pairs where applicable & I need to monitor the voltage....

Thanks for the replies and info.
Sure no prob

Sorry for the typo I meant to say that the batteries where 4.16 and 4.17v off my charger.
Oh OK that explains it.

I will discountinue use of my light as soon as the over-discharging protection kicks in (light shuts off the first time). I was at work and wanted to squezze out a little more light to check something.
Still... even with the protection circuit, its generally not the greatest idea to deplete the cells severely enough to "hit" the protection cutoff point. Protection circuits can & do fail, so relying on them solely to prevent over-discharge unfolds a layer of risk. The best approach is a 2-tier. Carry backup cells, and mentally monitor time length of use. Set a fixed time for yourself and after (say) 45 minutes, pull the cells and reload.

I just got a bored 6P from Oveready and will start using 18650s and just use my RCR123s on my single cell lights.
Thats a good idea. Less voltage does not necessarily mean less lumens. But its still not a good idea to regularly deplete single 18650 cells and bump them into their protection cutoff point. You should be aware that protection circuit cutoff points vary greatly from cell to cell. Many are WAY too low... in the vicinity of ~2.5V in some worst cases. So don't think for a second that a protection circuit alone is going to protect the cell.

I would still want to know the safe voltage difference I can use two batteries with different voltage. I used the two RCRs with the .17v difference and it worked fine but discountined use and just put the batteries in my single cell lights.
I can not answer this... as I only use equally charged cells in pairs.

I have noticed the two batteries also dont drain/discharge the same I have taken the batteries out and have seen a gap in voltage difference, so voltages are going to differ as one uses the flashlight at some point regardless if both batteries had the same voltage when off they came off the charger and put in flashlight.
That may be a correct observation, HOWEVER it still is NOT justification for using semi-depleted cells together with fully charged ones. Inter-mixing cells of varying depletion is a proven failure mode... not just on CPF mind you, other industries have also come to this conclusion. No amount of circular logic and reasoning can justify the use of Lithium Ion cells in a proven unsafe manner.

Just remember that there are no "absolutes" when dealing with Lithium cell safety. There is no direct 1-1 (100%) correlation between flame/venting and poor safety procedures. Its more like stacking the odds in your favor. With every miss-followed safety precaution, you are exposing yourself to another layer of risk. You are not going to completely eliminate that risk, but there are definitely things you can do to lessen it. If you choose not to follow proven safe practices... you may get away with it 1,2,3...100 times... but all it takes is once.

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Always test NEW batteries with a DMM ..........

the moment you remove them from the MAIL box .........

So you know the condition of what you just got .

They should measure about 3.85 volts / if not .... it should be investigated .

Draining them to cut-off point greatly reduces their lifespan , at minimum .

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