Storing Li-Ion - would this work

Due to upgrades and deals I shouldn't have taken, I have several cells that I am not using on a regular basis. It is the generally accepted wisdom around here that Li-Ion cells should be stored at 3.7v. Now, I have a very nice Xtar VP2 that allows me to set the charging voltage for 3.2v, 3.7v, and the ones that need to be charged to 4.13v. My manual says that the cutoff voltage for charging a 3.2v cell is 3.6v. My question is, would that work for charging my cells to a storage voltage level?

I don't see why not. I don't see how it can hurt anything. The only issue might be how long it takes. I'll try and explain.


I think for the first part of the charge or the CC, LiIon and LiFe charging is basically the same. You pick a current for example 1000mA, the charger charges with that current until it reaches very near or at 4.2V for LiIon or 3.6V for LiFe. The second part or the CV is going to be different. If you are charging a Lion as a Life the current will start stepping down at 3.6V not 4.2V. Way lower than the max voltage. I'm thinking this phase might take a very long time to terminate. I don't know what the termination amperage is on the XP2 but if it's low let's say .05mA or lower this could take a very long time. I am assuming that the XP2 is a cc/cv charger if not this is a non issue since it will just stop at 3.6V.


I'm going to try it. It seems like a good idea.

Hello Timothybil,

Recent discussions have indicated that storing at 3.6 volts may be slightly more optimal, but let's take a practical look at this.

With cells that are targeted for storage only I fully charge them, then discharge them at 1C. After the discharge at that rate the voltage will usually bounce up to the 3.6 - 3.7 volt range.

With cells that are stored but also act as standby emergency use I store them at about 4.0 volts and understand that it is less than ideal for storage. I offset that by knowing that these cells have about 80% capacity should they be needed.

Tom

If you have free space in your fridge and the wife won't complain then this will reduce the aging of the cells - http://batteryuniversity.com/learn/article/how_to_store_batteries
But the difference is neglible if stored at 40% charge.

SilverFox said:

With cells that are targeted for storage only I fully charge them, then discharge them at 1C. After the discharge at that rate the voltage will usually bounce up to the 3.6 - 3.7 volt range.

Tom

Click to expand...

What do you use to discharge 3500mAh 18650's at 1C?

Thanks

Hello Fmc1,

I use the West Mountain Radio CBA.

Tom

Tom


Cost wise that analyzer is not an option for me. Your 4.0V storage suggestion is interesting and I totally understand the logic.

Thank you for your response.


Frank

Hello Frank,

Another option is to pay attention to the run time in your lights. I use the analyzer because I am a geek. You can do the same thing by turning your light on and setting a timer. After a few tries you can dial in how much capacity you take from the cells and pretty much know what the voltage will be.

For example if you normally get around 2 hours of run time, 80% of that would be 96 minutes. That means that from a full charge you would use the light for around 24 minutes and end up with a cell with roughly 80% capacity left and it should have a resting voltage of close to 4.0 volts.

Tom

Tom

I have an MC3K so when I get home I'm going to make a storage program with a 4.00V target voltage.

Thanks

Frank