li-ion cell capacity

Whats the best way to find out an individual li-ion cell's capacity?

 

I was given some old laptop batteries to try replacing the cells into my dead laptop battery. That project never worked even with all cells at 4.2v but I found some cells appeared to charge up to 4.2v ok using my lipo cell charger and hold the charge. I am thinking of putting some together to maybe make a drill battery or led lights battery for next winter and need to know how can I test each cell's capacity so I can match them up.

Best way is to stick a load on them, see what they do.

 

Something like a car rear light bulb works well, as it will draw around 1a.

 

Then use a meter to measure current, and another to measure volts. See how long it takes to drop to 3.2 v

 

I've re-celled my drill and handheld VHF marine radio with old laptop batts, and I'm using those little Lipo buzzer things to monitor. Working a treat!

So if I put a 1a load on one, one at a time how long should I expect a cell to last aprox ? or is that irrelevant and I am simply looking for ones which last the same amount of time?

Use your lipo charger on discharge. Make a test jig like this to save time:

Thanks for the replies.

The diagram d8veh shows reminded me of my cree light's battery I was helped repair by removing the faulty bms electronics and replacing with 2s balance lead to charge using my lipo charger, which I guess is the same principal connecting the cells up.

So to practice with since its ready connected I used that which is 2s2p (which may complicate things) but charged it up to 4.2v each cell and found the discharge setting on my charger and set that to 1amp Mike suggested.

This took 2 3/4 hrs for 1 cell and 3hrs the other.

Am I right in thinking then this battery is a 2 3/4 amp battery (lowest)?

and if this was the laptop cells I could now pair the best ones together too.

Thanks for the replies.

The diagram d8veh shows reminded me of my cree light's battery I was helped repair by removing the faulty bms electronics and replacing with 2s balance lead to charge using my lipo charger, which I guess is the same principal connecting the cells up.

So to practice with since its ready connected I used that which is 2s2p (which may complicate things) but charged it up to 4.2v each cell and found the discharge setting on my charger and set that to 1amp Mike suggested.

This took 2 3/4 hrs for 1 cell and 3hrs the other.

Am I right in thinking then this battery is a 2 3/4 amp battery (lowest)?

and if this was the laptop cells I could now pair the best ones together too.

 

Yes, looks like the cell is 2.75ah@ about 1/3C rate. I expect at 1C it would be around 2.5ah (2500mah).