How often do you recharge unused 18650 batteries?

I'm curious; when you have a batch of 18650- batteries just sitting in a drawer, how often to you guys throw them on the charger to keep them topped off?

I tend to do so about every 3 months, but I don't really have a reason for that timing, so I wondered what others do.

It was my understanding that Li-ion cells are best stored at roughly half-capacity for long-term storage. (1 year+)

It seems a bit counter-intuitive, I know.

What kind of voltages are you seeing before you charge them ?

Never, best resting voltage is about 3.8V as far as I know (if you know you are not going to use them for a while put them in your fridge); I charge new batteries once and before I use them I check the voltage, only if it is under 4.0V (never happened) I would charge them again for normal use, for holiday or other occasions where full performance needed I would charge them to their max.

I've read that, but since I don't want to have to anticipate when I'll use them I always fully charge. I wonder how bad that is for them...

this is interesting - it claims store nicads discharged?!

http://www.rechargebatteryguide.com/batteries/how-to-store-a-rechargeable-batteries

anyone with long-term self-discharge graphs of our Protected XXXFire's, XTAR's, Sanyo's and what not?

Let's collect data points of Voltage (V) vs. progressed time (days) and draw a curve together :glasses:

I monitor my 18650's every couple of weeks making sure they don't fall below 3.7 volts. So far out of the 30 or so I own, none of them have

I store my bike light battery pack at about 45% in an airtight bag in the fridge for long term storage, but that's because of high cost to replace. Individual 18650 cells don't cost much so I don't worry too much about it.

How do you guys go about discharging cells if not through use in the lights?

Better read that table instead of my bad english xD

Battery Temperature

Permanent capacity loss when
stored at 40% state-of-charge
(recommended storage charge level)

Permanent capacity loss when
stored at 100% state-of-charge
(typical user charge level)

0°C

25°C

40°C

60°C

2% loss in 1 year; 98% remaining

4% loss in 1 year; 96% remaining

15% loss in 1 year; 85% remaining

25% loss in 1 year 75%; remaining

6% loss in 1 year; 94% remaining

20% loss in 1 year; 80% remaining

35% loss in 1 year; 65% remaining

40% loss in 3 months

http://batteryuniversity.com/learn/article/how_to_prolong_lithium_based_batteries

wow, thanks for posting that. Now I can spend the evening discharging batteries and putting them in the freezer lol

Wow. Thanks for sharing that chart.

The PERMANENT CAPACITY LOSS title really got my attention.

Every 2 months!

What I noticed, when I open an old laptop battery: lower the cell voltage better the cell condition,lower internal resistance, more capacity. That means, if a cell is for example 3.2V, surely will be better than an other which is 3.8V.

Interesting table. I guess that is another reason why I'm migrating toward AA batteries, both Eneloops and alkalines. A "discharged" 18650 battery is of no use to me whatsoever if the power goes out and I need it in a flashlight...that is why I top them off every few months.

But aren't almost all laptop batteries in a constant state of being "topped off" when the charger is plugged in? And I know a lot of people who always have it plugged in (including me). Now I am more confused than ever...

Also, we just got out first ActiveE, the all-electric BMW 1-series. You are supposed to top it off every night, and I think (not sure) that it uses Li-on batteries.

Note that best results for long term storage are at or slightly above freezing (Fridge), whereas storing below freezing is not recommended, per the rest of the battery university article.

Please remember that the chart is referring to cells that go UNUSED for long periods of time.

In the cases of both the laptop and the BMW, these are to be used frequently, if not daily.

I agree that the concept of long-term storage kind of goes out the window with 18650s, according to the chart.

The takeaway ? Rotate your stock of 18650s regularly !

Best advice is not to have too many batteries?

Who am i Kidding!!

We all have too many

Not all, one of my laptops did suggest that I used a special charge setting, where the batteries are only half charged.

Just check them from time to time , as long as the voltage is above 3.9v , I leave them alone ...

At 3.8v or bellow , toss them in the charger ... If there just being stored , ill pick a charger that terminated earlier [ WF-188 ] 4.15v area ...

But thats just me ...

And any battery that cant hold a charge = bye bye !

This does indeed apply to laptop batteries. If you use a laptop as a quasi-desktop & always plugged in then discharge to ~40% & remove it. Even if your laptop has a setting to maintain a persistent low charge the fridge is better. Unless you doing work & can't risk data loss who wants to lose lifetime on a expensive laptop battery?