Got given 6x18650 Sony Batteries. How do I know if they are good?

[jasonck08]

As the title says, I was given was given 6x18650 Sony Batteries. My dad gave me his old laptop battery pack from his Dell XPS m1210. It would only power up his notebook for 20 minutes or so (originally it ran for 2hrs+) I cracked open the battery pack, and was not surprised to find 6x18650 Sony 2400mah cells inside. 90% of laptops out there use 18650's. Mostly Sony's and LG's.

I checked all with my digital multimeter and they were all 4.10 or 4.11v. They all powered up a 1W LED just fine. In my experience when Lithium cells go bad, they don't produce any voltage.

Is there any way I can verify that these are good cells? I have a charger that I can charge them with and a DX VB-16 that can use 2xCR123A's or 1x18650, but I can not get the light to work with any of these batteries. It is about 1cm shorter than the 2 protected CR123A's.

The batteries are a year old, and went through about 50 full cycles.

 

[SilverFox]

Hello Jasonck,

Interesting, I wonder why they wouldn't work in your dads computer...

From what you have said, they look good. The next step is to do a discharge test on them. They are bare cells, so take care not to over discharge them. I would limit the discharge to a 3 volt cut off.

Then you can charge them up and see what voltage they end up at.

Packs usually fail when one cell becomes weak. You are looking for that weak cell or cells. There can be other reasons for the pack to quit working, but usually if a fuse or something like that fails, the pack will not work at all.

Good luck and let us know what you discover.

Tom

 

[jasonck08]

How should I discharge them? Should I get like a 5W bulb and just let it discharge and monitor the voltage with my digital multimeter? I don't have any expensive equipment...

Any guesses how good these Sony Cells are? Model is SF US18650GR 2400mah each. What kind of discharge current would these safely handle?

 

[SilverFox]

Hello Jasonck,

A 5 watt bulb should work great. Monitor the voltage when you hook the bulb up and compare it from cell to cell. Weak cells will show a greater drop in voltage. You can also do a runtime test and check how long the cell will last. Stop the test when the voltage of the cell reaches 3.0 volts.

The nominal voltage of the cell is 3.7 volts, so you are looking for a voltage, under load, close to that.

Normal Li-Ion cells are usually rated at a maximum draw of 2C. With your cells, that works out to 4.8 amps.

Sony makes good cells, but you may want to check the ID on the pack to make sure it wasn't involved in the recall of improperly manufactured Li-Ion cells.

Tom

 

[jasonck08]

Thanks for the tips SilverFox. Before ripping open I did a check to make sure the batteries were not on Dells recall list.

I'll try to test each battery to see whats up with them. I'll report my findings...

 

[jasonck08]

I discharged the first battery at .85 amps and runtime was a little over 2hrs from a starting capacity of 4.1. So the mah is at least 1800+. Now I'll try to charge up the battery and discharge another.