18650 cells in laptop battery packs

[mikekoz]

I have recently removed the 18650 cells from 3 laptop battery packs where the laptop they went to met untimely deaths! . Anyhow, two of these packs were not used a whole lot and the cells should be fine. In two of the packs, the cells all test at around 3.79V on my multitester. 6 of them I had to charge first, but they are all pretty consistent. 8 of them came from a high capacity pack (also not used too much actually) and they all test just over 4V. Why is this and how can I tell if these cells are protected or unprotected? Is there a way to see what the capacity of each cell is by looking at the specs for the pack? I am guessing some of them are 2200MAh as the pack was rated at 10.8v at 4400MAh. Any response would be appreciated!

Mike

 

[WildChild]

If they are all over 3V, they may be fine! They probably don't have the original capacity but may still be useful. About the capacity, you are right in your calculation. 10.4V at 4400mAh is two parallel rows of 3 cells. For sure, those cells are probably unprotected, the protection circuit being in the pack itself for them all (no individual protection for a laptop battery pack).

 

[DM51]

These cells sound OK, but they are unprotected cells - in other words it will be possible to overcharge or over-discharge them, so you will need to take care as they can be dangerous. If you have not had previous experience of Li-Ion cells, and unprotected ones in particular, you should do some research on them.

You will need to use a charger specifically designed for use with unprotected Li-Ion cells. The Pila IBC charger is one that is recommended - many other commonly available chargers fail to terminate the charge properly at 4.2v. When fully charged the cells will read 4.2v, and when empty 3.5v. Never let them exceed 4.2v or go below 3.0v.

 

[Bolek]

I also disassembld a laptop battery and I get 4 18650 cells OK (two 3.7V and two with 3.6 V) and two low i.e. 2.06 V. What if I recharge the two low with a DSD chargr ? Is it dangerous ? For somes of my aplications a low capacity will be OK but not a risk of fire or of explosion.

 

[WildChild]

I also disassembld a laptop battery and I get 4 18650 cells OK (two 3.7V and two with 3.6 V) and two low i.e. 2.06 V. What if I recharge the two low with a DSD chargr ? Is it dangerous ? For somes of my aplications a low capacity will be OK but not a risk of fire or of explosion.

Batteries discharged under 2.5V under high load, 3V-3.5V open voltage after resting suffered from internal damage. When charged it can heat up and explosion can happen. Li-Ion cells should never heat when charged. The 4 over 3V are probably still good but I would trash the 2 cells measuring 2.06V.

 

[DM51]

I recommend you recycle the two that are showing only 2.06v - they are probably dead. It might be possible to recover them, but this is a process involving among other things a measured slow initial rate of charge which you could not supply from your DSD (which BTW is not a good charger anyway). The cells at 3.6v and 3.7v are fine. Bear in mind, as with the others, these are unprotected cells.

 

[Bolek]

Thanks you. Is a low courent from a COURENT genarator OK , or a special charger requred ? What is a good value for the low courent ? For how long?

 

[Bolek]

It's going up very fast. U=3.16V after 2h at 5mA.:thumbsup: