I don't understand why these 18650 requires 0.5A during charge (laptop battery)

Batteries and Chargers Rechargeable Batteries
1

I just ripped some healthy used laptop battery pack that my friend donated to me

so I toss 2 of them into my Fenix ARE-C2 charger charging at automatic 1A charge
just around 2 hours and around 3.9v the cells starts to heat up badly

maybe I was doing things wrong or the cells are bad. I don’t know

2/6 cells died so I toss another 2 more into the charger (on different slots)
same case 3.8v batteries heating up (and vent a little)

with lots of fear and hope lost~ I tried charging my other cells that I own, nothing happen.
(even tried charging my friend’s unknown chinese 18650 cells no problem)

lastly I decided to block the bottom spring of my Fenix ARE-C2 charger to prevent the 1A charge and so far both cells topped up healthily

(Had done researches online telling me it’s safer to charge at 0.5A but 18650’s are usually charged at 1A because it’s not worth the time to wait?)

so what did I do wrong?

been pretty cool with small cells like 14500 and 16340 (as well as phone batteries) but this is my first time charging an 18650 from a laptop battery.

2

Did you check the cell voltage with a multimeter when they were hot?

3

I’m not 100% sure, but it sounds like the internal resistance of the batteries is high, so when you tried charging at 1 amp, that would’ve dropped resistance/current across the internal resistance. That was also probably why the batteries got warm/hot.

I think that those batteries may be bad or unsafe, but maybe someone else can tell you for sure.

4

Sanyo cells?

5

Generally speaking it’s better to charge at .5 anyway. But I have to say I’m curious what cells these are. Would you please take a picture of them for us? What I’m guessing though is that these batteries are just shot. The internal resistance has probably gone up from use or from abuse. It’s one of the reasons why you don’t want to discharge any lion too far. You can often get them to charge back up but if you do it over and over Crystals form in the batteries themselves and this causes the internal resistance to go up. When that happens either charging or discharging at higher amps can be dangerous.

For safety sake I would not use them. However if you post a picture it’s possible that someone can tell you more about this particular battery. It might just be a good battery that was made for lower amp applications and you would be fine using them in a setup that only requires low amps.

6

High temperatures and charging Lithium Ion cells are a bad mix.

7

I have seen this with at least a dozen laptop pulls. IIRC they were all Sanyo cells, 2200 or 2600 mAh. I just figured the internal resistance had gone way up. I just sent them to a recycle bin.

8

what was the starting voltage?
red sanyo’s are the worst for doing this when left sitting overdischarged.
just recycle them.

9

wow
thank you all for the replies
really appreciate it.

yup I did
they were 3.8v on fenix charger meter and 3.6v on dmm while it’s burning my hands as I hold it lolol
what do they tell?

bad or not I guess I had to recycle all of them since none of these could hold any charges anymore (despite being a healthy used pack of laptop battery)

yup
red sanyo cells


Sanyo L
UR18650A N16A

I wouldn’t say they are fully discharged?
when I rip them off all cells are above 3.7v or more
nevertheless all cells are bad at holding its charge now as it took the cells to drop from 4.2v to 3.6v in less than a day (even the healthy ones I claimed)

I guess my last step is to recycle all of them

Anyway thank you all very much for the help and education in 18650 cells :smiley:
Really really appreciate it

some pics before recycling these cells