Question about storing batteries

[derek10]

Hi
I always read to store batteries to 40% (~3.8V) when they are about to be stored for a long time to reduce permanent capacity loss while avoiding overdischarging (less than 3V) due to self-discharge.

I saw a test here which can't remember the author nor link in CPF that tested an unprotected Li-ion for years and barely self-discharged.

Will storing them up to lower but safe voltages (3.1 - 3.3V) lenghten their lifespan compared to 3.8V if regularly checked (i.e twice a month) and charge if needed to counteract self discharge and avoid overdischarging?

Or 3.8V is the ideal Li-ion storage (i.e the chemicals are more "relaxed")?

Thank you

 

[Dr. Mario]

I would prefer to hold it at 3.7 - 3.8 Volts (40% charge) for some reasons, as the older the Lithium-ion batteries get, the higher internal resistance get, the more pronounced self-discharge become. That way you have cushion in term of self-discharge - any lower, it may go too far to be recovered if left alone for too long.

And it also depends on temperature of where you're intending to store those batteries in, you don't want it to be kept at above 110 F (45 C) or above, and / or below 0 F (-32 C), as it affect the self-discharge factors, as well as the survivability of the batteries being stored away. And, yes, unprotected Lithium-ion batteries don't self discharge as much because there's no protection board to sustain (ie. keeping the built-in circuit breaker closed).

As for 3.2 Volts Lithium Iron Phosphate cell, I don't think it's really necessary to keep it at 40% charge, as I have left it at 100% charge for several months, there's not so much of any noticeable problems with this battery being left that way.

 

[mcnair55]

I always follow the makers instructions works out fine for me.

 

[derek10]

Thanks

I would prefer to hold it at 3.7 - 3.8 Volts (40% charge) for some reasons, as the older the Lithium-ion batteries get, the higher internal resistance get, the more pronounced self-discharge become. That way you have cushion in term of self-discharge - any lower, it may go too far to be recovered if left alone for too long.

And it also depends on temperature of where you're intending to store those batteries in, you don't want it to be kept at above 110 F (45 C) or above, and / or below 0 F (-32 C), as it affect the self-discharge factors, as well as the survivability of the batteries being stored away. And, yes, unprotected Lithium-ion batteries don't self discharge as much because there's no protection board to sustain (ie. keeping the built-in circuit breaker closed).

As for 3.2 Volts Lithium Iron Phosphate cell, I don't think it's really necessary to keep it at 40% charge, as I have left it at 100% charge for several months, there's not so much of any noticeable problems with this battery being left that way.

I am talking more about regular Li-Ion batteries, I currently don't have any LiFePO4 powered device

But if the batteries are new and you monitor them on a regular basis to avoid overdischarge, will storing them below 40% further extends their shelf life? or is 40% just the best threshold for best shelf life?

I always follow the makers instructions works out fine for me.

Does any device maker specify the best voltage to store batteries in the long term :S

 

[ven]

Ideally 3.6-3.8v will do, mine can be anywhere in between the V for cells that are stored long term(more than a few month, so back up or spare cells).

Lights in use but not daily use(maybe weekly) are locked out to minimise any parasitic drain...........but are charged up ready for use.

Apparently there are benefits of storing in a cool place(like a fridge) for long duration's, they need to be in an air tight container to minimise risk of condensation though. This method is not convenient for me, nor do i find it necessary. What ever works for you really...............

 

[MAD777]

I pondered this storage question and have decided to keep all my batteries fully charged. Here are the reasons:
I want my lights ready to go at all times.
Although their life may be somewhat shorter, they are replaceable.
It seems battery technology is advancing so fast that I buy a better battery every time I purchase a flashlight. (Dead batteries give me opportunity upgrade)

Note: the above does not conform to a budget philosophy, it's purely a flash-a-holic viewpoint.

 

[Dr. Mario]

I'd agree about leaving it at 100% - if you store it at 100% for a month, the modern Lithium-ion batteries would probably not care (as they use better electrolytes). It's usually best that way so you can always be prepared for any emergency (ie. power blackout), not to mention it's occasionally cheap to buy new batteries (dead battery = excuse to upgrade to new and better batteries).

 

[Gauss163]

I'd agree about leaving it at 100% - if you store it at 100% for a month, the modern Lithium-ion batteries would probably not care (as they use better electrolytes).

Even though there may have been slight advances since the older degradation studies, one can probably still obtain significantly more lifetime by employing charging strategies that minimize the time that the cells spend at high voltages and temperatures. Whether or not that is worth the effort is for each individual to decide, taking into account their personal context.

 

[Dr. Mario]

Gauss163, I definitely agree.

 

[MidnightDistortions]

I usually just keep them charged. If they got at least 80% that's a good starting point and i never had any trouble with this. If the cells were well taken care of they should last a long time. If you are not planning to use the batteries for a long time then i suggest getting primaries and then you can keep a real small amount of rechargeables.