I acquired 6 used li-ion cells 1 year ago. Since I wanted to know for certain how well the cells would hold a charge after 1 year, I conducted an experiment. I recently tested the cells. Below is some data related to my testing:
Voc = 5.25 (Open circuit Voltage--no cell in charger)
Imax = .68A (max charge current=680mA--no cell in charger)
Manuf: Panasonic Id: CGR18650CE V: 3.6 (nominal) mAh: 2150 (typical capacity when fully charged) +Chrg: CC=1.43A (max), 4.2V (max) // "+Chrg"=Charging -Chrg: CC=2.04A (max), cut-off @ 3V // "-Chrg"=Discharging
- All cells were charged at a CC=.68A to a CV=4.2V. Charging was cutoff when the charge current reached .01A@4.2V
- The resting V of all cells after 24 hrs was at least 4.05V.
Here are the cell measurements after 1 year of resting:
Cell V___ A___ VA(W) Est mAh (i.e. VA/3.6*1000) 1 4.16 3.29 13.67 3802 2 4.01 3.23 12.95 3598 3 3.95 3.18 12.56 3489 4 3.85 3.09 11.90 3305 5 3.95 3.17 12.52 3478 6 3.77 2.95 11.12 3089
The multimeter was verified to be operating properly using a bench power supply.
We can see from the data that some cells held their charge better than other cells. My question is, how can the cells have such a high capacity when the datasheet indicates their capacity is 2150mAh? I know the cells are at least 5 years old. I also realize that my estimated mAh capacity is not based on actual discharge tests, but is there some other way of estimating the capacity of such cells using a multimeter & a bit of math?