I keep 2 sets of LG MJ1 batteries fully charged (ie to 4.2V):
Set #1: 3 batteries EDC’ed in my belt pouch along with my Wurkkos FC13, which is my backup light + main powerbank;
Set #2: 3 batteries HDC’ed in my hiking backpack, along with a Fenix ARE-D1 charger/powerbank;
The idea is to always have power not only for the flashlight itself, but also (using its powerbank functionality) for recharging cellphone/satcomm/HT when I’m away from home.
The issue is that I know Li-Ion batteries shouldn’t be kept unused at 4.2V for very long, and while the batteries in Set #1 get used pretty frequently (at least once a month), the ones in Set #2 are hardly used at all: so far I haven’t needed them, but I keep carrying them (along with the Fenix ARE-D1 to operate as backup powerbank) in case I get into Real Trouble™ in the field, like getting stranded for a long period, or forget to charge the batteries in Set #1 and get surprised in the middle of nowhere exactly when I need them to recharge some piece of essential equipment.
So, I’m thinking of swapping sets #1 and #2 so they both get used, and I’m thinking about doing that once a month (which means each battery would be used at least once every two months).
What do you think, is this a good strategy? Can an interval longer than 2 months be used without taking a toll on these batteries?
Doing as you say and swapping the cells will mean that set #2 cells will spend more time at a lower state of charge, which theoretically would be an improvement over always being at 4.2V. But then set #1 will spend more time at a higher charge. At least they’ll age more evenly?
State of charge, rate of charge, temperature, and time are the factors that seem to matter in regards to liion longevity.
I think you’re misunderstanding me, or perhaps it’s me misunderstanding you. The idea is that both sets would be kept at close to 4.2V most of the time (as I always recharge batteries as soon as I make it back home), but with the rotating, they will not be left for long at that state: they will be regularly cycled (each battery at least once every 2 months).
The time spent at either end of the spectrum (fully charged or fully empty) is what causes (faster) aging, sounds like your proposal will just spread the “relief” between the two cells.
Don’t stress about it if that’s your set-up that works for you, assuming you’re in the US, cells are quite reasonably priced.
You could charge “only” to around 4V, the difference between 4.0 and 4.2 doesn’t represent much capacity.
Don’t stress about it if that’s your set-up that works for you, assuming you’re in the US, cells are quite reasonably priced.
That’s the problem, I’m not (years-long road trip in South America) and the logistics for getting US stuff here are quite expensive and complicated .
You could charge “only” to around 4V, the difference between 4.0 and 4.2 doesn’t represent much capacity.
Thanks, I haven’t thought of that! This is doable, and actually even easy with my MC3000 charger (just change the “Target Voltage” parameter in the acting program).
Do you have any info or preferably a reference as to how much this would help extend the cell’s life?
I assumed you only had that Fenix charger. In that case you’re golden. I’m not a battery guru, so I don’t have any references, there are plenty discussions on here about “optimal charge voltage”.
This topic has been debated many times. On one hand you can spend hundreds of hours making sure you get every life minute out of your $5 battery. Or you can basically do nothing, keep them fully charged and focus on some more important thing in life. There is no evidence that suggests rotating them will make them last longer, there is no evidence that suggests keeping them at a storage voltage will make them last longer.
The Fenix was for a long time my EDC charger/powerbank (carried in my belt purse), now moved to my HDK due to the FC13 consolidating its powerbank function. At home the MC3000 is king, but it’s a little too big and heavy to either EDC or HDC
there are plenty discussions on here about “optimal charge voltage”.
Thanks, will try and fnd them! it would be lovely if someone like @HKJ or Mooch or someone similar did a long-term test of batteries while keeping them at the same charge and discharge levels, but I guess that’s asking too much…
Edit to add: I concur that there’s a lot of time/energy spent on what are essentially disposable items, however, OP not in the states so harder to procure new cells. Not everyone has luxury we do
There are many whitepapers related to this subject.
“In general, temperature is the most significant stress factor, where deviations from the typical 25 °C can lead to accelerated failure. Higher SoC operation accelerates degradation, due to the relationship between the electrode potentials and the rate of parasitic side reactions, while higher current operation increases the likelihood of failure, due to mechanical stresses developing in the battery during cycling, but also promotion of lithium plating during charge.” [source]
State of charge, rate of charge, temperature, and time are the factors that seem to matter in regards to liion longevity.
Rate of discharge and depth of discharge matters much less, from what I have read in other studies.
Lower storage voltage and lower temperatures results in less capacity loss over time. There is not a significant benefit to storage voltages below 3.7V at normal (~25C) temperatures:
Even if they did last longer, do we know how much longer? If I told you maintaining your batteries at storage voltage vs not doing so will make them last 10 years instead of 9, is that worth it?
A $5 battery over the course of 10 year converts to 50 cents per year. Dont tell me your time is not worth more than that.
But you must realise there are countries outside of the US where cells are not $5? Or where there are strict shipping regulations, or lower income, so even if it was “only” $5, that’s a lot of money…
I don’t have time to delve into the journals right now, but I expect the capacity loss Vs storage voltage numbers (in a scientific setting), are quite well measured for the more mature lithium chemistries.
See below. But I would like to know the number with some certainty anyway, whether its 9 vs 10 or 4 vs 5 or whatever.
A $5 battery over the course of 10 year converts to 50 cents per year. Dont tell me your time is not worth more than that.
You must have missed this:
So it’s not only way more expensive (like $50 for express shipping even a small packet via a courier company or traveller-for-hire, plus up to a month of waiting due to customs and whatnot), plus a lot of time and effort spent to arrange everything.
And even if I were in the US, there’s also a matter of principle: if I can sacrifice a little bit of my time to send one less battery every N years into a landfill and consequently force more lithium, cobalt, manganese, iron, etc to be mined and steel to be produced and energy spent on making and transporting a new one and etc, I will happily do so. Pachamama not only deserves but is also in sore need of every bit of help we can afford her.
Charge to 4.1 get two times the life cycles. Charge to 4.0 get four times the life cycles. NASA did a study probably three plus years ago with 18650s and they automatically terminate all charging at 4.1 volts. They tested the mj1 and the q30 and the Sanyo /Panasonic GA
and I think about two others. Replacing the cells in their equipment in space is not an option. So they have ruled out charging to 4.2 volts. I believe from memory they stopped discharging at 3.3 volts. And I think that was under load. It was a very interesting study and I wish I could find it again. Different batteries did better under certain conditions. I think overall they decided the mj1 was best for their purposes. I seem to recall it being a constant charge and discharge with a minor rest possibly after discharge to simulate solar powered charging and then many hours of darkness on the panel every day. Nothing good happens at 4.2 especially just sitting.
If only more people thought like that…
But, and just a thought. In your situation it might be good to be proactive. Meaning get a second full set of cells and store them at around 3.8 volts. Rotate the sets once per year. Then do what you mentioned with rotating the cells in the active group…
and think about terminating charge at 4.1 volts.
I know it would be expensive, but if it is a matter of survival, it may be worth it.
At least, if you did it now when there is no stress about doing it…i.e you can afford to wait a while to get the cells.
All else being equal, you would be set for many years. Is it worth ~$100 and a couple of months of wait time. Well that is up to you.
I just spent close to $1000 to buy a set of solar 200 watt panels and a 1000 Wh “Solar Generator” just to make sure I could run some essentials in case of power outages. I wouldn’t die if I could not run those things. It could be different if you were lost somewhere in the Amazon Jungle with no power… yes?
So save Pachamama, yes. But save yourself is also important.
So Mandrake50 you are recommending a person spend more money even though they clearly want to save money?
Is this your conclusion?
So you are saying that we should purchase batteries with the same mindset as you with your solar panels.
Do you use your solar panels for emergencies or recreation? Do you use your solar panels for emergency lighting or walking your dog?
As you can see, you really should not be making general statements about your personal lifestyle as it may not be the same as your audience’s lifestyle.
