Batteries, crystal growth and fridges

[bbb74]

Ok I've got 3 questions about storing NiMH rechargeables (LSD Maha Imedions if you have to know)

Note- Where I live, the daily temperature cycles between about 10 and 20 degrees (celsius) during winter and 18 to 30+ in summer.

1. When cycling a shelf queen with a Maha C9000, I would generally have thought I should just use the Refresh&Analyse mode then discharge back down to 40% for storage (following Battery University's advice here). But this charges the battery before discharging it. Wouldn't it better to discharge it first to try to break up whatever crystals have grown while in storage, rather than charge it and make those crystals bigger (increasing the risk of separator damage)?

2. Regarding putting batteries in sealed bags in the fridge. I have a frost free fridge (which tends to dry things out) and I store the batteries in a closed (but not 100% airtight) compartment inside the fridge. If I put the batteries in a sealed bag, won't this guarantee the batteries are stored long term at 100% humidity, as the initially warm air in the sealed bag is cooled in the fridge so given generally humid outside conditions, the bag insides will be at 100% due to being cooled?

Wouldn't it better to store them un-bagged in the fridge, but then bag them for a couple of hours when coming out of the fridge so condensation from the warm outside air forms on the bag instead of on the battery?

3. I store some shelf queens in the fridge, and I cycle them every 2 months or so. But I'm wondering if I should store any batteries I'm not going to use for more than a couple of days in there as well, particularly in summer when its normally 30+ degrees celsius? Does the thermal stress of being cooled down regularly damage the battery through expansion/contraction? I figure that the stress of the fridge would be less than that of daily 10+ degree cycles outside of the fridge?

 

[Battery Guy]

Ok I've got 2 questions about storing NiMH rechargeables (LSD Maha Imedions if you have to know)

Nice cells from what I have seen.

Note- Where I live, the daily temperature cycles between about 10 and 20 degrees (celsius) during winter and 18 to 30+ in summer.

Noted.

1. I store some shelf queens in the fridge, and I cycle them every 2 months or so. But I'm wondering if I should store any batteries I'm not going to use for more than a couple of days in there as well, particularly in summer when its normally 30+ degrees celsius? Does the thermal stress of being cooled down regularly damage the battery through expansion/contraction? I figure that the stress of the fridge would be less than that of daily 10+ degree cycles outside of the fridge?

I don't know what a "shelf queen" is.

Storing NiMH cells in a refrigerator is a perfectly legitimate thing to do. The lower temperature will reduce self-discharge rate and all other chemical degradation mechanisms that result in irreversible capacity loss will be slowed down.

Seriously, the lower temps are not going to hurt your Imedion NiMH cells. If you want to reduce the self-discharge rate of your cells by storying them in the fridge, then by all means go for it.

2. Regarding putting batteries in sealed bags in the fridge. I have a frost free fridge (which tends to dry things out) and I store the batteries in a closed (but not 100% airtight) compartment inside the fridge. If I put the batteries in a sealed bag, won't this guarantee the batteries are stored long term at 100% humidity, as the initially warm air in the sealed bag is cooled in the fridge so given generally humid outside conditions, the bag insides will be at 100%?

You don't need to worry about your batteries "drying out" in your frost free refrigerator. The inside of the battery is at 100% humidity, and the seals are designed to keep the water inside the battery under a huge range of humidity conditions.

Personally, I would not store them in a bag or any other container where condensation might occur. Condensation on the outer surface of the cell might cause corrosion, and this might lead to big problems. Always avoid exposing the exterior of your cells to liquid water.

Wouldn't it better to store them un-bagged in the fridge, but then bag them for a couple of hours when coming out of the fridge so condensation from the warm outside air forms on the bag instead of on the battery?

Whatever technique avoids exposing the exterior of the cell to condensation is probably the best technique.

Cheers,
BG

 

[bbb74]

BG-

By shelf queen I mean I bought too many batteries for what I needed at the time, so I have some I am not using (yet). Trying to treat these the best possible way so when I do get around to using them over the next year they will be in good condition.

To clarify, I was concerned about condensation on the external surface of the batteries, not about "drying them out"

Cheers.

 

[StarHalo]

Fridge storage will only make a notable difference in non-LSD NiMHs, with most other types of cells you're looking at a roughly 5% difference in discharge over time, and every time you need a new battery, you'll have to wait for it to reach room temperature before using it. Not really worth it in my opinion.

 

[bbb74]

Fridge storage will only make a notable difference in non-LSD NiMHs, with most other types of cells you're looking at a roughly 5% difference in discharge over time, and every time you need a new battery, you'll have to wait for it to reach room temperature before using it. Not really worth it in my opinion.

I'm not doing it to reduce self discharge, I'm doing it for longevity of batteries I don't need yet (have too many). The theory is you get less large crystal growth.

 

[Battery Guy]

I'm not doing it to reduce self discharge, I'm doing it for longevity of batteries I don't need yet (have too many). The theory is you get less large crystal growth.

Storing any cell in the refrigerator will reduce the rate of side reactions that slowly degrade performance. So keeping your extra cells in the fridge will improve longevity.

Not sure about your crystal growth theory. I have seen people talk about crystal growth in NiMH cells before, and I think that this idea is a carryover from NiCd technology. In an NiMH cell, there is no dissolution and precipitation of the active electrode materials, so there is no growth of any crystals. However, several materials inside the cell do corrode over time, including the metal hydride alloy, and storing the cell at a lower temperature will reduce the rate of this corrosion.

The bottom line is that there is really no reason not to store your extra Imedions in the refrigerator, and doing so will improve longevity over storing them at room temperature.

Cheers,
BG

 

[qandeel]

BG

Thanks for the good info. Is this also true for eneloops?

The bottom line is that there is really no reason not to store your extra Imedions in the refrigerator, and doing so will improve longevity over storing them at room temperature.

Cheers,
BG

 

[45/70]

Storing any cell in the refrigerator will reduce the rate of side reactions that slowly degrade performance. So keeping your extra cells in the fridge will improve longevity.

I can go along with that. Most any degradation involving a chemical reaction will occur more slowly at reduced temperatures.

Not sure about your crystal growth theory. I have seen people talk about crystal growth in NiMH cells before, and I think that this idea is a carryover from NiCd technology. In an NiMH cell, there is no dissolution and precipitation of the active electrode materials, so there is no growth of any crystals.

I don't believe this is entirely correct. While it's true that NiCd cells suffer more from "memory effect", NiMH cells do also, but to a lesser extent. Although NiMH technology has greatly improved nickel based cell resistance to the formation of abnormally large crystal formation because of the absence of cadmium, it still occurs in NiMH cells. From B.U.:

[FONT=Verdana, Arial, Helvetica, sans-serif]When introduced in the early 1990s, nickel-metal-hydride was promoted as being memory-free. Today, we know that this chemistry is also affected but to a lesser degree than nickel-cadmium. The nickel plate, a metal that is shared by both chemistries, is partly to blame. While nickel-metal-hydride has only the nickel plate to worry about, nickel-cadmium also includes the memory-prone cadmium plate. This is a non-scientific explanation why nickel-cadmium is affected more than nickel-metal-hydride. [/FONT]

I have actually witnessed the breaking up of these crystal formations while discharging both NiCd and NiMH cells on a CBA at very low discharge rates. The associated voltage fluctuations can actually be "seen" while watching the realtime graphing, as the formations break up. The difference between NiCd and NiMH cells is also evident. It is clear that NiCd cells suffer from this condition to a greater extent than NiMH cells, but it is also quite obvious, that NiMH cells are not immune to this condition.

I'm not doing it to reduce self discharge, I'm doing it for longevity of batteries I don't need yet (have too many). The theory is you get less large crystal growth.

bbb74, to prevent large crystal formation, the best solution is to store cells in a discharged state (~1.20 Volt OC), whether at room temperature, or in the fridge.

"Memory effect", or the formation of abnormally large crystals, is primarily caused by self discharge, excessive trickle charging, or lack of exercising cells. While storing cells in the fridge will slow self discharge, it does not eliminate it and, the need to exercise cells still exists, it just doesn't have to be done as often. Also keep in mind that provided the memory effect isn't too severe, it can usually be corrected through cycling, or reforming the cell.

Dave

 

[Battery Guy]

I don't believe this is entirely correct.

I fear that we will go too far afield if we get into this discussion. Suffice it to say that I agree 100% that voltage depression (aka memory effect) occurs in NiMH cells. However, with respect to "crystal growth" in NiMH, we will have to agree to disagree for the moment.

Perhaps worthwhile to start a new thread on the topic if there is interest.

Cheers,
BG

 

[45/70]

...... However, with respect to "crystal growth" in NiMH, we will have to agree to disagree for the moment.

Agreed! Gotsta go for now.

Dave

 

[MikeAusC]

I store NiCd and NiMH in a discharged state and now find they last much longer.