18650 Voltage Question

I currently have two 18650 batteries 3500 mAh (Eastshine) and 2600 mAh (Fenix USB). Both are protected button top batteries. I use an Eastshine battery charger. After recharging both batteries, my multimeter shows that each one measures at 4.1 volts. I have read several articles about overcharging Lithium Ion batteries. Some say the optimal voltage after a charge is 4.2 v other articles say do not exceed 4.2 volts to avoid damage. Anyone offer some guidance. Is 4.1 OK or should it be higher?

I b retired said:

I currently have two 18650 batteries 3500 mAh (Eastshine) and 2600 mAh (Fenix USB). Both are protected button top batteries. I use an Eastshine battery charger. After recharging both batteries, my multimeter shows that each one measures at 4.1 volts. I have read several articles about overcharging Lithium Ion batteries. Some say the optimal voltage after a charge is 4.2 v other articles say do not exceed 4.2 volts to avoid damage. Anyone offer some guidance. Is 4.1 OK or should it be higher?

Click to expand...

"Some say..." It's not a question of opinion, the standard used by the Big 5: Sony, Panasonic, Sanyo, LG and Samsung, is to charge to 4.20v (+/- .05v,) so 4.15v-4.25v is where we want to be, erring on the lower side to increase (slightly?) cell life. Nobody can really quantify empirically, how many cycles would be gained/lost by consistently charging to either extreme, so call it a wash.

Undercharging doesn't really hurt, except in runtimes.

Chris

I think you also have to make sure the device measuring the voltage on the battery is accurate or not a it can either make the voltage lower or higher. 0.1v is about 0.25% of 4.2v but depending on the individual battery could add up to considerably more in capacity.. perhaps 200ma on the 3500mah battery so on a 100 min runtime could add up to another 5 minutes perhaps.

Charging to 4.1V is absolutely fine. You'll not get the last few percent of capacity, but your cells will live longer if you don't kill them some other way.

I have seen a study of charge voltage vs. capacity and vs. cycle life. IIRC, the difference between 4.1 and 4.2V was less than 10% capacity and more than 20% in cycle life. But that's a laboratory test that assumes the cells are treated well in all other respects. As ChrisGarrett suggests, nobody knows how you use your cells, so nobody can tell you how long they will last.

Maybe some other CPFer can remember where that was?

Another possibility is the accuracy of your DMM ?

If the 4.1V is correct, and you don't need every last bit of capacity, that will be easier on the cells.

I personally do not usually charge my Li-Ion up to the max.

High quality batteries are fairly common and prices have dramatically even gone down, and even that of high quality, safe chargers....personally I wouldn't really worry about termination voltages and life cycles...I haven't even finished one cycle life of one cell since I started in this hobby 7 years ago!

Relax and have fun.

It's not so much the peak voltage, but the time (and temp) while near max that tends to degrade the battery. I have had Li-Ion cells lose ~ 40+ % function within a couple years, mostly in devices that get hot and/or spend lots of time at max (like mobile phone, tablet, laptop, etc)