AW 18650 Batteries stored in a safe.

I have a Surefire (actually it is the predecessor to the Surefire – Laser Products) dedicated weapon light for an 870 shotgun. I've only had to change the CR123 batteries three times in the last twenty years. Most of the time, the shotgun sits in safe and comes out only for an eight hour shift once in a while. The safe gets pretty hot, at least in the upper-eighties to mid-nineties.

I just purchased a light that uses an 18650 battery for an M4. The flashlight is mounted to the M4 on a picatinny rail and so taking the light off and putting it back on when needed is possible but not the best situation.

Is it safe to keep that type of battery in the flashlight in the safe and how long could I expect them to last without recharging? Is there a reasonable chance of the battery causing a fire in the safe? Like I said I have had CR123 batteries in there for over twenty years without any problems but evidently from what I have been reading, these rechargeable li-ion batteries are more sensitive and I don't want to take any chances. Any help would be greatly appreciated.

Hi kt50,

The 18650s are more sensitive to heat and cold than a CR123 but in different ways than you may have been led to believe. LiCo (li-ion) cells have a better track record for overall safety around here than CR123s. The heat will wear out an 18650 more rapidly, and the cold will reduce it's performance more significantly (during the cold), but either way, unless the temps are really extreme, there is no massive increased risk of fire danger. CR123s have the advantage of holding their stored energy through heat and cold for up to 10 years.

A properly charged and discharged LiCo 18650 from a reputable manufacture has a much lower risk of fire/explosion than a CR123 in most conditions IMO.

Li-Ion cells will generally not loose much as far as state-of-charge in a year (depends on many factors, like the parasitic drain of the PCB, self discharge will increase with cell aging), however, the natural aging process will knock off an unrecoverable portion of the cells maximum capacity. In an elevated temperature environment, the natural aging process is sped up, so rather than say, a cell lasting 5-7 years, it might last 2-4 years (just a guess) in your application.

Think of laptop batteries, and how they are always about useless after the first 2 years or so, it's from the heat of the laptop.

If you expect to use the light frequently, charge the cell to ~4.10-4.20V, if you expect it could be stored for long periods of time, charge to ~3.9-4.0V instead, this will help maximize shelf life of the cell.

-Eric

Eric,

Thank you for the very informative post. I am not too concerned about the batteries longevity as I am for safety. You have put my mind at ease. A big mahalo and aloha from Hawaii.

Ken