easilyled
Flashaholic
It just occurred to me that I don't really know the answer to the question above.
Can someone chime in please?
Can someone chime in please?
It just occurred to me that I don't really know the answer to the question above.
Can someone chime in please?
I use this chart and depending on how much I use of my flashlight I play it by ear and when I get a chance I check the voltage. I dont let my batterries go lower than 3.8V. Also some drop-ins will flash/flicker to let you know the voltage is low and some batteries have overdischarge protection.
LiIon Battery Charge Status
4.2V – 100%
4.1V – 87%
4.0V – 75%
3.9V – 55%
3.8V – 30%
3.5V – 0%
This chart that floats around CPF is reasonably accurate, except for the 3.5v figure.
Also when discharged down to 0% or pcb cut off. Charge them up as soon as possible. But you probably already know this.
You bring up a good point, Jason. Also, it was mentioned long ago by, I believe SilverFox and probably others as well, that estimating the remaining capacity of traditional LiCo cells is a bit harder at voltages of ~3.80 Volts and below. This is due to minor differences in the actual chemical composition and physical construction of different manufacturer's cells.
Also, I've found that particular chart to be on the low side. I think this one is a bit more accurate, most of the time.
4.2V – 100%
4.1V – 90%
4.0V – 80%
3.9V – 60%
3.8V – 40%
3.7V – 15–20%
3.6V – basically discharged
Even this one seems conservitive sometimes, however I think it's pretty close with older/used, conventional LiCo cells.
When you get into other chemistries, it gets even more complicated. Even LiMn/IMR cells are quite different. They start out about the same, but as the OC voltage gets lower, they're pretty far off. I estimate my AW 18650 cells, for example, to be at about a 60% SOC at 3.75 Volts OC, but are still able to maintain higher voltage under load than LiCo cells with a higher OC voltage. And when you get into LiFe/IFR it's even worse. The discharge curve for these cells is so flat, that it's really difficult to estimate remaining capacity, at all.
Dave
I'm confused by his use of the qualifier "or pcb cutoff" which would indicate he meant functionally flat. That is, his use of "0%" meant when a battery's protection cut-off tells you there's no more juice left and not really when there is literally no juice left.Most of the Li-ion cells I've tested using a CBA II have shown very little capacity left below 3.2V.
Mike moderator007 was saying that flat Li-ions should be charged ASAP, 40% is far from flat and is as you say the ideal level for storage. I store my spare cells at about 3.7V to 3.8v in a sealed plastic food storage box in the fridge.
Norm
I'm confused by his use of the qualifier "or pcb cutoff" which would indicate he meant functionally flat. That is, his use of "0%" meant when a battery's protection cut-off tells you there's no more juice left and not really when there is literally no juice left.
Are you saying it's unsafe to store Li-ion batteries at their cut-off or below cut-off?
Here is some interesting info about the effect on capacity of 18650 li-ion cells in long term storage at different SOC levels and at either 23 degrees C or 45 degrees C.
These curves are based on 18650 cells with graphitic anodes, such as the Panasonic NCR18650 has:
Those charts are interesting, and they highlight the fact that with lithium ion cells there is a 0% state of charge (say about 3.3 V open circuit), and there is a less than 0% state of charge (below 3.3 V in the Sony example).
With no automatic protection or cut-off for IMRs, its not easy to know what to do for the best sometimes.
Something that hasn't been mentioned, while Li-Ion cells do not exhibit much self discharge, if a cell is stored in a zero SOC, at this level of charge, the voltage will drop exponentially fast, whatever the reason. . . . . .
Unfortunately my Milwaukee 28v Li-ion battery pack hasn't seen that graph because it's refusing to charge beyond 23.8 after ~5 years of storage in a shed. It was never charged...just stored as a spare while I used the first battery pack.The Sony graphs above show that there is no problem storing cells at 0% state of charge.
If you discharge a cell to cut off at 2.7 volts, the voltage will recover once the load is disconnected.