Long term storage of NiMH: 40% charge?

[Cemoi]

According to Cadex website about batteries:
the NiMH should be stored in a cool place and at a state-of-charge of about 40 percent

Since the same page deals with LSDs (New chemical additives improve the self-discharge but at the expense of lower energy density) it seems this recommendation applies to both non-LSD and LSD batteries.

It puzzles me that this figure (40%) is exactly the same as that recommended for long term storage of Li-Ion, on many webpages including Cadex website.
How come two different chemistries should be stored with exactly the same state of charge (which does not appear to be an approximative figure, since the recommendation is 40%, not "half-charge")?

Any other sources (manufacturers?) for the recommended state of charge for long term storage of NiMH (standard and LSD)?

 

[Niconical]

If someone did store nimh at 40%, it wouldn't be 40% for very long.

Even LSD will gradually be going down.

In fact, the whole point of LSD Nimh is to be able to store them at a starting 100% and for them to specifically not go down to 40%.

 

[Dan FO]

Don't believe everything you read on a website.

That company (Cadex) makes chargers and analyzers, not batteries.

 

[Turbo Guy]

The lower the state of charge the slower the chemical reactions. The slower the chemical reactions the longer they last. Reduced temperature slows both the chemical reactions and the self discharge rate.

Last week I removed 8 Sanyo NiMh AA 2700s and 8 sanyo gree sleeved 2500s from refrigerated storage. They had been there for three years and they are al in excellent condition.

I have a small frig. set at 45F which is used just for battery storage. I have thousands of dollars worth of LiPolt,LiFePO4 along with a bunch of Nicad and NiMG cells and batteries.

Cells/ batteries are sealed in zip lock freezer bags. I remove the bags containing cells I need ,let reach room temp. remove the cells/ batteries , charge or discharge to storage level,place back in bags and frigerate till needed again.

 

[TakeTheActive]

Don't believe everything you read on a website.

From my Sig Line LINKs:

Minimize the Aging Effects on Your 'Storage Box Queens' by Storing Them PARTIALLY Charged - SilverFox​

 

[Cemoi]

That company (Cadex) makes chargers and analyzers, not batteries.

After reading most of their pages I hadve the feeling that Isidor Buchmann has a good knowledge of the different battery chemistries, which seems a requisite if you want to design sophisticated battery chargers and analysers. And I feel like buying his book.

Last week I removed 8 Sanyo NiMh AA 2700s and 8 sanyo gree sleeved 2500s from refrigerated storage. They had been there for three years and they are al in excellent condition.

What was their initial and final state of charge?

Minimize the Aging Effects on Your 'Storage Box Queens' by Storing Them PARTIALLY Charged

Thanks, very informative. I'm surprised though that Tom doesn't mention storing the batteries in the fridge, like many others seem to recommend on CPF and elsewhere.

 

[Turbo Guy]

What was their initial and final state of charge?

In at 1.10

When removed 0.95 to 1.05



OT Few here know me but many on RC groups,Wattflyer and RC Universe know me rather well but by a different user's name.. I have flown radio controlled aircraft since 1963.First flew electric ones 30 years ago and have flown only electrics for over 4 years. We place a lot higher demands on our batteries. I charge LiPolys at 3C,LiFePO4 (true A123 Systems ones) at up to 10C. Discharge rates are around 10C average with burst up to 60C. It takes more than just hit and miss battery management to have batteries survive at these performance levels. Many of my LiPoly batteries cost between $85 and $165 each and I have many of them.

Two of my flashlights use LiFePO4 cells. An original 5C Mag now has 2 LiFePO4 cells a fill spacer and Mag LED . A Husky 36 watts handhelp spot has 2 LiFePO4 cells in place of the original 6V 3AH PB. It takes me approx. 15 min. to charge eithier of these.

Please do not misunderstand. I am not saying CPF members do not know about batteries,just stating a little background info.

 

[LIGHTSMAD]

The lower the state of charge the slower the chemical reactions. The slower the chemical reactions the longer they last. Reduced temperature slows both the chemical reactions and the self discharge rate.

Last week I removed 8 Sanyo NiMh AA 2700s and 8 sanyo gree sleeved 2500s from refrigerated storage. They had been there for three years and they are al in excellent condition.

I have a small frig. set at 45F which is used just for battery storage. I have thousands of dollars worth of LiPolt,LiFePO4 along with a bunch of Nicad and NiMG cells and batteries.

Cells/ batteries are sealed in zip lock freezer bags. I remove the bags containing cells I need ,let reach room temp. remove the cells/ batteries , charge or discharge to storage level,place back in bags and frigerate till needed again.

which of these batterys can i freeze for long storage and if so what % should i freeze them at, in or out of the freezer:

AW18650 lion =
AA eneloops NiMh =
5 1/2D cell pk 3500mah NiMh =
AW18500 lion =

 

[Cemoi]

In at 1.10

Thanks.
This is way below 40% state of charge, problably more around 10%?
Sounds like a good way to store for long term, since they have almost not self-discharged in three years (hence very little, or no harmful crystalline formation).

 

[Turbo Guy]

This is way below 40% state of charge, problably more around 10%?

Perhaps . A little math

If I take a fully charged high quality,healthy AA NiMH and discharge it at say 500 mA (0.5A) to .9 volts and let it rest for say 10 minutes it will read approx. 1.0V.

Most such cells when discharged at 0.5 -1.0A or 0.25 - 0.5C end up with approx. 10 to 20% charge remaining in them I would guess. Standard discharge rate to determin capacity if 0.2C.

How many post required before one is allowed to post attachments?

data points from a very recent 8 cell Eneloop discharge of mine at .25A

MAh discharged / volts under 0.25A load
625 / 10.1 =1.2625 per cell
1,125 / 9.89 = 1.236
1,150 / 9.6 = 1.2 per cell
1,750 / 9.05- 1.131

1750/2000=87.5%
1750/2100-83.3%
so 1.13 per cell under a moderate(?) load is close to 15% at least in some cases.




Charles

 

[Turbo Guy]

which of these batterys can i freeze for long storage and if so what % should i freeze them at, in or out of the freezer

I believe that if you check such places as Battery University and others listed in the Sticky you will find ideal storage temp. 0 C / 32F. I use 45F and have for years.

 

[VidPro]

what he said, turbo used all the methods for proper storage and recovery, freezing the "electolyte" would be a bad thing, you know how freezing causes expansion.

Turbo on the attachments, are you trying to post pictures? if your in "advanced" mode do you see the yellow picture icon? does it work?
because pictures here are usually hosted offsite, and posted with the img code . i am not so good at it myself, but i have not seen restrictions applied., other than the forum doesnt host pics, or should i say, has never hosted mine

 

[StarHalo]

+1 for fridge storage of batteries, glad to see someone else who gets it..

Many household freezers are below 32F; when storing batteries it's better to err on the side of above freezing rather than below it, so the refrigerator is your best bet. Right around 40F (the average refrigerator temp) and a Ziploc bag is as good as pragmatic battery storage gets.

My father worked at a pro camera store for many years, they would place storage/unstocked film and batteries in a basic home refrigerator in the back room. So if you buy your batteries from a professional enough business, they've already been stored in a fridge..

 

[SilverFox]

Hello Charles,

We don't host pictures on this forum. I use Photobucket, and others use something similar.

To insert pictures you use the img command inside brackets [ ] followed with the /img command once again insuce brackets [ ].

Tom

 

[Mr Happy]

Perhaps . A little math

If I take a fully charged high quality,healthy AA NiMH and discharge it at say 500 mA (0.5A) to .9 volts and let it rest for say 10 minutes it will read approx. 1.0V.

Most such cells when discharged at 0.5 -1.0A or 0.25 - 0.5C end up with approx. 10 to 20% charge remaining in them I would guess. Standard discharge rate to determin capacity if 0.2C.

How many post required before one is allowed to post attachments?

data points from a very recent 8 cell Eneloop discharge of mine at .25A

MAh discharged / volts under 0.25A load
625 / 10.1 =1.2625 per cell
1,125 / 9.89 = 1.236
1,150 / 9.6 = 1.2 per cell
1,750 / 9.05- 1.131

1750/2000=87.5%
1750/2100-83.3%
so 1.13 per cell under a moderate(?) load is close to 15% at least in some cases.

I'm afraid I can't understand what is being described in this post -- I don't follow what is being calculated and what the numbers mean.

However, my own experience with Eneloops in the C9000 is that discharging them at 500 mA down to 0.9 V gives close to 100% of their available capacity. A second discharge at a lower rate produces negligible further mAh.

Secondly I find that the voltage of a discharged cell always rebounds to 1.2 V or more. If a discharged cell has a voltage less than 1.2 V after several minutes of rest then I think the cell is not healthy.

 

[LIGHTSMAD]

which of these batterys can i freeze for long storage and if so what % should i freeze them at, in or out of the freezer:

AW18650 lion =
AA eneloops NiMh =
5 1/2D cell pk 3500mah NiMh =
AW18500 lion =

?

 

[VidPro]

which of these batterys can i freeze for long storage and if so what % should i freeze them at, in or out of the freezer:

AW18650 lion =
AA eneloops NiMh =
5 1/2D cell pk 3500mah NiMh =
AW18500 lion =

dont FREEZE.
the idea is put them in a sealed Bag, preferring to remove the air from the bag, then put them in the refridgerator, not the freezer.
Especially not the freezer on your normal refrigerator because it does defrosting and cycles many degrees back and forth, the cell will be virtually tortured instead of heped out.
and
not in a Deep freeze, because you could damage the cells as many deep freezers could freeze the electrolyte, not to mention again wild swings on power outages, and expansion and contraction of the parts and pieces that make up the item.
then also remember the seal on a li-ion is designed to GIVE on pressure, and expansion and contraction of gasses can cause negative or positive pressures in the cell, damaging it.
Also as a side note, someone froze a battery with protection, and for some strange reason it broke the protection.
THEN
when you remove the cells from the cooler storage, you should always bring the SEALED bag of them back to room temperature, otherwise you could get condensation (like water forming on the outside of a cold glass) and the condensation would get in all the wrong places.
so always bring the still sealed item back to room temperatures about, before breaking the seal open again.

and you also have to concider the storage time, and the level of discharge prior to storage, AND make sure that any parasitic draw from anything (in this case the protection) does not discharge the cells while they are parked.

THEN
you gotta add in, that you would not want to store FOOD in a item you stored a li-ion battery, these toxic gasses permiating your food, that would be really heathy if something was going wrong you didnt know about.

THEN
if your bag seal was poor, and the li-ion had/got a flaw, and moisture was seeping into the cell, reacting to the lithium.

gee anymore problems i might have missed?

if it cant be done 100% properly, then it isnt even worth thinking about doing it.

 

[LIGHTSMAD]

dont FREEZE.
the idea is put them in a sealed Bag, preferring to remove the air from the bag, then put them in the refridgerator, not the freezer.
Especially not the freezer on your normal refrigerator because it does defrosting and cycles many degrees back and forth, the cell will be virtually tortured instead of heped out.
and
not in a Deep freeze, because you could damage the cells as many deep freezers could freeze the electrolyte, not to mention again wild swings on power outages, and expansion and contraction of the parts and pieces that make up the item.
then also remember the seal on a li-ion is designed to GIVE on pressure, and expansion and contraction of gasses can cause negative or positive pressures in the cell, damaging it.
Also as a side note, someone froze a battery with protection, and for some strange reason it broke the protection.
THEN
when you remove the cells from the cooler storage, you should always bring the SEALED bag of them back to room temperature, otherwise you could get condensation (like water forming on the outside of a cold glass) and the condensation would get in all the wrong places.
so always bring the still sealed item back to room temperatures about, before breaking the seal open again.

and you also have to concider the storage time, and the level of discharge prior to storage, AND make sure that any parasitic draw from anything (in this case the protection) does not discharge the cells while they are parked.

THEN
you gotta add in, that you would not want to store FOOD in a item you stored a li-ion battery, these toxic gasses permiating your food, that would be really heathy if something was going wrong you didnt know about.

THEN
if your bag seal was poor, and the li-ion had/got a flaw, and moisture was seeping into the cell, reacting to the lithium.

gee anymore problems i might have missed?

if it cant be done 100% properly, then it isnt even worth thinking about doing it.

so basically i can fridge all of these different battery types,
i'll double zip lock them to be extra safe!

i suppose rougly 40% charge for NiMh/NiCd and 3.9V for the lion's is ok!

 

[VidPro]

so basically i can fridge all of these different battery types,
i'll double zip lock them to be extra safe!

i suppose rougly 40% charge for NiMh/NiCd and 3.9V for the lion's is ok!

yes , mabey 3.8v for the li-ion if you know the (protection) discharge rate, or if you just check it every 6months.

 

[Cemoi]

deep freezers could freeze the electrolyte

What is the freezing temperature of a NiMH electrolyte?
Probably not 0°C = 32°F because - assuming it is an aqueous solution - it is not pure water hence a different freezing temperature.