18650 Storage

So guys, when my batteries run low and I swap in charged ones, is it ok to charge the depleted ones so they'll be "ready" for the next change or is it not advisable to charge them and leave them stored?

For me I've 10+ of 18650 batteries and I keep them charged and on standby because I know the charging of such batteries takes a long time. I use these batteries daily.

Assuming standard LiCo cells, if you will be storing them for months they like to be stored at about 60% of charge, which is about 3.7v IIRC. If you use them regularly then go ahead and charge them up. If you do store them for a long period remember to monitor the open circuit voltage every few months.

Optimal storage for lithium cells is at 3.6-3.7V - they will live longer.

But they only live for 3-4 years normally regardless of usage so I'm not too bothered by the theoretically lowered lifespan. I have some 5 year old 16340s but they only have round 100mAh capacity left so are hardly useful. If I'm not going to use them for a while I discharge them to storage voltage, but it takes quite a while to balanc charge them back up - I always use the balance charge for multi-cell lights but this is not necessary for single cell lights.

It is useful for testing, you know that all the cells have the same level of charge. It is tedious waiting for them to balance though.

If you store them at 40% charge at 25C they will lose 4% per year.

If you store them at 100% charge at 0C they will lose 6% per year.

So there is no real reason to bother with the 40%, I keep mine charged (at 4.17V or less, so not really 100%) in the fridge, so I can use them whenever I need them and not 5 hours after.

I would feel really stupid if there was an outage (or I otherwise needed the 18650s immediately) and they would all be at 40% to avoid some 1-2% theoretical capacity loss per year.

I have the red/black flame protected Trustfire cells if that matters.

I like the way you think. I'm a cyclist and I have two 18650 torches + two bar lights with 4x18650 cell packs. Night riding for me is a recreational activity ( can't commute) during the fall and early spring when there's not enough daylight after work to get in our normal rides. So I really need to store the batteries for several months at a time. After much discussion and reading a great article on the subject from Battery University, Here's what I do: Based on known run time, run out the batteries to around 45%, Place in sealable zip-lock bag along with one of those moisture absorbing packets, note the storage date on bag, place in vegetable bin in the fridge. This should be around 35 degrees F, which is pretty close to 0 C. Downside is the batteries need to 'thaw' for 12-24 hours before charging, and I need to take them out and run this scenario over again every 2-3 months. I do this with the bar lights because they do have a higher cost. I don't figure the single cells cost very much so I keep them charged and ready to go in case I need them for this time of year. 2-3 years is all I expect to get out of them and they're cheap to replace.

As I get closer to summer and peak riding season, all my Lion batteries are going in the fridge. I have several good AA torches for emergency use.