Gday folks … ive recently grabbed my first few torches to use rechargeable batteris, namely the Li-Ion 18650 and 26650 protected type batteries.
My question - I want to keep one these flashlights in my car … but we are approaching summer here and it gets bloody hot in my car after its been sitting in the sun all day at the train station … id say 50 degrees celcius on occasion, possibly more
Is this safe?
Also what are the optimum and min/max temps for storing these types batteries?
Simple answer Li-on’s hate heat.
Lithium-ion suffers from stress when exposed to heat, so does keeping a cell at a high charge voltage. A battery dwelling above 30°C (86°F) is considered elevated temperature and for most Li-ion, a voltage above 4.10V/cell is deemed as high voltage. Exposing the battery to high temperature and dwelling in a full state-of-charge for an extended time can be more stressful than cycling.
50 degree safe but it reduce useful life of li-ion batteries. specially when you keep cells fully charged state.
better way is keep one or two cells in car and others in home.
I keep my unused batteries in fridge (put cells to ziplock bag for prevent moisture damage)
Thanks mate … in that case i think i’ll just leave my cheapo AAA torch in the car then
Also, i take it you are saying that it is also not advised to keep Li-ion batteries fully charged?
Can anyone recommend me something cheap that i can use for testing the voltage level … as you can no doubt see, im still a dead set noob when it comes to electronics
fully charged li-ion + high temperature = reduce life
keep ready to use batteries fully charged
keep unused batteries 40% charge (voltage of 3.80V) for reduce degrade.
charge li-ion battery to 4.1V instead of 4.2V will reduce capacity by 10-15% but increase cycle life.
to measure battery voltage, you can use cheap DMM (under 10:money_mouth_face: or battery voltage monitor (under 5:money_mouth_face:
Thank you very very much 
Guess I shouldn’t have kept my tenergy 18650s in the garage over the summer. It would reach 90° plus in there in the summer.
I use Energiser Ultimate Lithium AA and AAA primary cells (dated 2018) in my car torches … I test them by switching them on and off (for a few seconds) about once or twice a year … I have put Energiser Lithiums in all my household remotes as well and they are dated 2025 … As far as i am concerned , these are “fit and forget” batteries … Sometimes when I check the torches in the car , one might not work … It is always due to a battery connection … I take the batteries out , rub the ends on a piece of dry rag and then put them back and they work again … Probably I should do an annual maintenance on the car torches (clean and lube) but they are sort of out of sight and out of mind.
One of my car torches uses three AAA’s and the other uses one AA … I also carry a spare set of lithium primaries in the glove compartment just in case they are ever needed.
I always have an ITP A3 (titanium) on my car keyring and another ITP A3 (stainless) on my house keyring … Also always clipped in my inside pocket is an ITP A2 … All the ITP’s are fitted with Eneloops , but they don’t get subjected to high temperature.
So , I would recommend Energiser Lithium primary cells to leave in the car … They are a bit more expensive than the other alkaline cells and they don’t seem to leak.
Good luck