Since discovering this forum I have purchased a few flashlights that take 18650 batteries. I have also purchased about a dozen quality batteries, all of them either Keeppower or Panasonic protected. They don’t get a lot of use, I have to recharge them every 6 to 8 weeks. How many years can I expect these batteries to provide good service?
I was thinking about adding to my battery inventory but I read in another post these batteries only last one or two years. For me that seems like a short life for such expensive batteries with very few charging cycles. Is this true, or did I misunderstand the other post? I may have to reconsider future flashlight purchases if it is true.
The typical life expectancy is 500 full recharges. Partial cycles only count as a percentage from all I can gather and the cells do better with small discharge/recharge cycles than full ones. That said, many cells are already a year or two old when you get em.
I’ve got laptop pulls that were new, unused, but 6 years old and with enough charge in em to recharge in a normal fashion and they’re still going strong in multiple lights. So as long as they’re kept in a cool dark place away from environmental hazards such as high humidity they should be good for quite a while.
And they won’t leak in your lights and turn em into garbage.
You can look at this way. If the cell costs $10 and you get 500 recharges before you need to replace it then that is about 2 cent for each recharge. If you only have to recharge it once a month then you’ve spent 2 cents each month. At 500 months that’s 41 years for each cell. I think the cells will die of old age first.
The above is true if you’re treating them right. A general rule of thumb from data I’ve seen on this and other flashlight boards is that you don’t want to discharge them below 50% before recharging them. I saw a chart for a Sanyo 18650 with a 1 or 3 amp load you need to recharge them before they hit 3.8V. That’s the best I could determine from the information that I came across.
You can discharge them down to zero percent and even below with a load but the lower you discharge them the more you shorten their life and the greater the chance of damaging them. If you discharge below 2.7V (some say 2.9V) then the cell is most likely heavily damaged and you should recycle it. You have to decide how much risk you’re willing to take for $10. Do a Youtube search on thermal runaway for Li-Ion batteries if you haven’t already.
Have you been checking the voltage with a DMM?
There are only rules of thumb to increase cell longevity because of variation in the manufacturing process, differences in material quality used in each cell, and other factors too numerous to list here.
41 years? Um, no. Besides the number of cycles, there is also calendar life to consider. Even unused Li-Ion batteries are basically finished after a few years.
A slight variation on your question could be how to make the batteries last as long as possible.
I try to use as few li-ion batteries as possible. Usually only one set of batteries for the flashlights I currently use the most. And I try to use up a battery and discard it, before I start using a new battery. Spare batteries I store cool and dry in my cellar. Partially discharged. I believe 3.6 volts is optimum, but as long as it is above 3.6 and not over 3.9, I think it is fine.
When the capacity of a battery is too low, perhaps 50-75% of the capacity when new, I discard it and get a new one. I buy a few batteries every year to keep some spares handy.
For nimh eneloop I do the opposite. I try to rotate among all of the batteries so they all get some exercise at least twice a year. And store them fully charged. Every Christmas/New Year, I run all the nimh through a refresh cycle and check capacity, and discard the ones with lower capacity. If I buy new nimh I start using them straight away.
I and many others have countless cells that are many many years old, new unused stock, that are perfectly fine. When were the Moli 26700s made - wasn't it something silly like 2008? It's highly unlikely we wouldn't have heard about it if there were any duds from that batch. I got 60 Samsung 28As from new old stock laptop packs that were assembled in 2010 (cells themselves must be older than that). Nothing wrong with a single one of them.
Low temperature (5C/42F) and low voltage (under 4V) will help to increase the longevity of unused cells. The effects of time on cell aging and the sensitivity to voltage and temperature will vary from one model of cell to another and this may be something to note when considering different cells if longevity is important to you.
That being said, even if you are storing your cells at 4.2V at room temp (25C/75F), you’re generally looking at well under 10% loss of capacity per year.
Only recently has it become possible to easily test capacity of li-ion batteries. New analyzing chargers that automatically test capacity. I discarded a bunch of old li-ion batteries after I tested them...
That's great and all, but real world says different. Lots of us have lots of 'too old to still work and should be discarded' cells and I can't remember anyone mentioning that any of the cells are showing any problems. Believe me, we would know about it. Everybody would know about it. I mean, just look at some of the threads where an incorrect sticker found its way onto an otherwise normally functioning cell, it would never end and we'd all be sick of seeing threads about how these crappy old cells aren't worth the trouble. There aren't any of those threads.
I got 20 Panasonic CGR18650D's from BLF member ReverendJim a few years ago. The date code is E8517. I was told they were made in 2009. So far they've been great. I'm doing a capacity test on a couple I use on a regular basis right now. I'm pretty confident they're pretty close to their 2350 mAh rating
As long as the batteries still are fine with good capacity, they are naturally good to use. My point was that only recently did it become easy to actually measure the capacity.
Li ion loses life for three reasons, age, state of charge and drain/charge cycles. The charge drain cycles should get you about 500 cycles, so no worries there, temperature is kind of annoying, the warmer they get the quicker they will age, when not in use i keep most of my batteries in the basement where its cooler (only two stay upstairs in flashlights). At room temp and above they start aging faster, there is a battery university chart out there with more information. State of charge is the most annoying, li ion cells will age slowest if kept at 40% charge (3.8V) but this is unpractical for everyday use. So keeping them topped up will hasten their demise, hence i only have two fully charged and in flashlights. My general rule of thumb is to keep them all batteries at 40-60% charge and charge them up when i need them except for the sacrificial ones i use regularly, and when they die i will sacrifice two more.
I have over 100 Li-ion cells, mostly 18650. I have over 60 lights. All my lights have charged cells, all my spares are charged, all at room temperature (usually around 80 degrees F)
I guess I’m a Pro at killing these nice cells…
I know I have several lights that seem hell bent on destroying the things! They drain em fast and deep, get em hot. Man, I’m GOOD at this!
Dang sure didn’t buy em to see how long they could sit in a basement.
Why are you re-charging them if you are not using them? Li-on keeps it charge quite well.
1. Quit charging and topping them off if you aren’t using them consistently. That’s one of the worst things you can do. Store in a cool spot at 3.8v if you aren’t using them. Avoid heat, that INCLUDES lights that heat up badly. If you can’t hold it > it’s killing your battery.
There is a real fetish in this group for POWER. As long as you know this is taking a toll on your batteries, go for it. Just don’t be surprised.
DBCstm is a ‘poster child’ for how to minimize battery life. He obviously knows it and is fine with it. :bigsmile:
2. Do not discharge below 3.2-3.4v. Do not ever discharge below 3.0v. I know, some of the protected cells have cut-off below that. I consider that to be bad design. Companies are not in the business to maximize the life of your products most of the time.
I know they’re gonna have a shorter life because of it, just like drag racing an engine. But it’s what I build them for. I want to hear them SCREAM!
You don’t hear the guys at the racetrack fretting over how many gallons of fuel is being burned. Or the cost of the tires they smoke off before every run with bleach poured on the ground. It’s part of the game.
Now, Hot Rod flashlights might not be what everybody is looking for. That’s fine. Get a surefire and live happily ever after. Me? I’ll still keep twisting their arms behind their backs til they beg for mercy! :bigsmile:
A small light like the Eagle Eye X6 making 6.77A with 1560 lumens, doing 82.75Kcd, oh yeah! (There are modes of course, for when the screaming causes headaches) And new technology is giving us better cells all the time, why keep the old ones forever?
The Race is ON!
(I actually do have an Eagle Tac TX25C2 that isn’t tortured. De-domed, nice thrower with the new XP-L, but not power tweaked. I know, right? Hard to believe but it’s true.)
