Li-ion Cells, Good or not good?

[GoldStar611]

Hi, I have 4 Li-ion 18650 cells by Sony(US18650GR) that I pulled from my laptop battery. The laptop stays on a maximum of 5 minutes and then shuts off (windows power monitor and such are disabled so software should be a problem).
I "tested" each cell by using a DMM set on amperes and each battery would give at least 17 amps (I was afraid of shorting them longer than just a second, so I say at least 17 amps). How can I tell for sure if these cells are any good? Oh, yes, I have an original thread in another subforum that didn't get much attention: http://www.candlepowerforums.com/vb/showthread.php?p=2635166

 

[Mr Happy]

Eek!

Don't short Li-ion cells. That is certified mistreatment.

To test the cells you can measure the resting voltage. If the voltage is between about 3.5 V and 4.1 V, you can charge a cell in a suitable charger designed for Li-ion cells. When you take the cell off the charger on completion the voltage should be about 4.2 V. Let it rest a few hours and see if the voltage stays at 4.2 V or drops. If it drops below 4.0 V the cell is probably at end of life (someone can correct me on the exact voltage drop to be concerned about).

There are other more complicated tests you can do but that is the basic one.

 

[GoldStar611]

I'm thinking the batteries are gone.. Does anyone else have any furthur tests I can do for these guys?

 

[greenLED]

How old is that battery pack? Li-ion batts degrade over time. In a battery pack, usually one of the cells go bad while the remaining still have some life in them.

The solution, of course (and assuming you know what you're doing when it comes to li-ion battery chemistry) would be to replace the spent cell.

Careful, though! Those cells are most likely unprotected, which means if you subject them to any more torture they might blow up on you. Then there's the issue of safely soldering onto "bare" cells, etc.

A simpler alternative would be to buy a replacement li-ion battery.

 

[GoldStar611]

The solution, of course (and assuming you know what you're doing when it comes to li-ion battery chemistry) would be to replace the spent cell.

Well, I'm not much for mixing old/new batteries, and eventually the other cells will degrade as well and I'd be here again. I plan on replacing all the cells at this point, and doubling the capacity while I'm inside.

Careful, though! Those cells are most likely unprotected, which means if you subject them to any more torture they might blow up on you. Then there's the issue of safely soldering onto "bare" cells, etc.

A simpler alternative would be to buy a replacement li-ion battery.

I usually don't settle for simple, and I'm pretty sure they are not protected as there are sensors all over the place in the batt pack. The new cells don't have tabs on them, so I'll be thinking of ways to affix tabs to them. Any idea here? Low heat solder perhaps?

 

[mdocod]

have you tested the open circuit voltage of the cells after a charge and after resting them for awhile as Mr Happy has suggested? Start with this. Then move on to rebuilding or replacement options. It's possible that the cells are fine, and your laptop is just too stupid to know it. (I know this sounds stupid, but most stupid things are stupid like that)