I have some 18650 Li-ion AW rechargable's. I was wondering if it was better to let them run down some before recharging or to charge them more often? I don't know much about batteries but some old batteries would develope a memory if you charged them without running them low. I would like to do whatever is best for the battery.They also say they are 3.7V--2200mAh
Battery Storage
- Thread starter jpdr350se
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coppertrail
Enlightened
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- May 21, 2006
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Battery University suggests that Li-Ion cells be stored with a 40% charge.
Anders
Enlightened
Found by using search option :shrug:
http://www.candlepowerforums.com/vb/showthread.php?t=218759&highlight=liion+storage
Anders
http://www.candlepowerforums.com/vb/showthread.php?t=218759&highlight=liion+storage
Anders
Fallingwater
Flashlight Enthusiast
rechargeables.
The title suggests you want to store them long-term, but the post suggests you want to use them. Which is it?
Anyway: store them at 40% in the fridge, and charge them whenever possible when actually using them. LiIon cells don't like full discharges.
HDCharlie
Newly Enlightened
Please excuse my ignorance, but how does 3.75 volts equate to a 40% charge on a 4.2 volt cell? I just don't know how that number is calculated. 
As if you couldn't tell, I'm pretty new at this. I'm much better with Harleys.
As if you couldn't tell, I'm pretty new at this. I'm much better with Harleys.
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SilverFox
Flashaholic
Hello HDCharlie,
Welcome to CPF.
I don't think it was calculated... just observed.
Tom
Welcome to CPF.
I don't think it was calculated... just observed.
Tom
HDCharlie
Newly Enlightened
Not to be obstinate, but I can't get my head around 40% equaling 3.75 volts. I really don't mean to be a PITA, just trying to learn.
I think I got it. 40% of X does not equal 3.75 volts. 40% of X just happens to be at 3.75 volts. Maybe?
Thanks for the welcome. :thumbsup:
I think I got it. 40% of X does not equal 3.75 volts. 40% of X just happens to be at 3.75 volts. Maybe?
Thanks for the welcome. :thumbsup:
Last edited:
coppertrail
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Charlie -
I believe this was from a post Tom made a while back.
"You can get a pretty good idea of the state of charge of Li-Ion cells simply by measuring the resting voltage. Resting voltage is with the cell disconnected from the circuit and left to stabilize for 10 minutes or more.
A very close (conservative) approximation gives...
4.2V – 100%
4.1V – 87%
4.0V – 75%
3.9V – 55%
3.8V – 30%
3.5V – 0%"
I believe this was from a post Tom made a while back.
"You can get a pretty good idea of the state of charge of Li-Ion cells simply by measuring the resting voltage. Resting voltage is with the cell disconnected from the circuit and left to stabilize for 10 minutes or more.
A very close (conservative) approximation gives...
4.2V – 100%
4.1V – 87%
4.0V – 75%
3.9V – 55%
3.8V – 30%
3.5V – 0%"
Fallingwater
Flashlight Enthusiast
Resting voltage is not directly proportional to remaining charge. There's an equation someone made to get a somewhat precise percentage of remaining charge, but I can't find it right now.
SilverFox
Flashaholic
Hello HDCharlie,
Several people involved in RC airplanes did a bunch of testing and and came up with the numbers that Coppertrial posted. Their usage involves higher current draws, so it is a conservative approximation for our applications.
In the 1 - 2C current draw range I have found that
4.2 is 100%
4.1 is about 90%
4.0 is about 80%
3.9 is around 65%
3.8 is around 48% and
3.7 is around 40%
The equation that Fallingwater is referring to, I think, is this
State of Charge in % =
100(0.1966+sqr rt(0.0387-1.4523(3.7835-Vcell)))
Tom
Several people involved in RC airplanes did a bunch of testing and and came up with the numbers that Coppertrial posted. Their usage involves higher current draws, so it is a conservative approximation for our applications.
In the 1 - 2C current draw range I have found that
4.2 is 100%
4.1 is about 90%
4.0 is about 80%
3.9 is around 65%
3.8 is around 48% and
3.7 is around 40%
The equation that Fallingwater is referring to, I think, is this
State of Charge in % =
100(0.1966+sqr rt(0.0387-1.4523(3.7835-Vcell)))
Tom
HDCharlie
Newly Enlightened
Thank you all. I have a better understanding of the number now. I think I better brush up on my electricity basics. It's been a long time.
45/70
Flashlight Enthusiast
While not directly related to the OP's original question, but nonetheless related, I think this is a good place to mention that the overall fitness of LiCO Li-Ion cells can be determined by voltage as well.
After being charged to 4.20 Volts on a proper charger and let rest until the voltage stabilizes:
4.20 Volt = 100%
4.10 Volt = 50%
4.00 Volt = Time to replace
Dave
After being charged to 4.20 Volts on a proper charger and let rest until the voltage stabilizes:
4.20 Volt = 100%
4.10 Volt = 50%
4.00 Volt = Time to replace
Dave
coppertrail
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That is correct, they do not develop memory. But just like your cell phone, sometimes they'll run all the way down, nothing you can do about it. With the protection circuits, it won't harm the battery.
45/70
Flashlight Enthusiast
No, Li-Ion's do not develop memory. That is a nickel based chemistry problem.
Part of the reason Li-Ion storage is discussed frequently, is the fact that they age whether you use them or not. It is true, if you maintain a 40% state of charge, regardless of ambient conditions, they will age the slowest, cooler being better, however.
As for charging them, you can "top them off" whenever you want. Of course, the farther away (either direction) you are from 40%, the faster they will age. Personally, I just charge them up to 100%, keep them in the fridge, and use them in rotation. I wouldn't worry about it too much. Hey, they're meant to be used!
Dave
Part of the reason Li-Ion storage is discussed frequently, is the fact that they age whether you use them or not. It is true, if you maintain a 40% state of charge, regardless of ambient conditions, they will age the slowest, cooler being better, however.
As for charging them, you can "top them off" whenever you want. Of course, the farther away (either direction) you are from 40%, the faster they will age. Personally, I just charge them up to 100%, keep them in the fridge, and use them in rotation. I wouldn't worry about it too much. Hey, they're meant to be used!
Dave
