Nimh degrade with age?

[bcwang]

Does anyone have any knowledge on whether unused Nimh cells degrade with age? Lets say you grab a unused sanyo 2500mah cell now that was made when they first came out, do you think it would give you the same service life and performance as one made now?

This is something to think about before buying and stocking up too many batteries.

[mightysparrow]

It's my understanding that 1) yes, they do generally degrade with age, all else being equal; and 2) the battery technology and manufacturing quality of new batteries improves over time as well.

[SilverFox]

Hello Bcwang,

A NiMh cell will gradually completely self discharge. When it does that, it oxidizes on the inside and dies.

If you keep some charge on the cell, it can last 3 or 4 years, but may not immediately charge up to full capacity. You may have to do several charge/discharge cycles to bring it back up.

The proper way to store NiMh cells is to discharge them at 1C to 1 volt per cell, then store them. Every 30 days put the cell through a charge/discharge cycle to keep them vibrant. I do not know how long you can keep cell this way, but I have around 5 years on some NiMh packs and they are still going strong.

On the other hand, I have noticed that occasionally a battery manufacturer will comment that cells are good for 2 years, then should be replaced.

I have not seen any formal testing on this, but this is about the best I have been able to come up with. If you replace your cells every 2 years, you should always have equipment that works well. If you stretch things out, you may have to do some of your own testing to determine when the cells drop below 80% of their initial capacity, indicating time to replace the cells.

Tom

[bcwang]

This kind of sucks for me. I have probably at least 50 more nimh cells that are unused and getting old, some as an 1800mah would be when they first came out.

This would explain why some of the cells that I start putting into service are not performing up to par. I have to stop buying batteries!!!!! It's so hard though as new ones keep coming out before I got to finish using old ones.

Now another thing, with cells like eneloop that might not self discharge to completely empty anytime, do you think they'll have a much longer lifetime?

[Marduke]

Old cells can still be useful in non-critical applications. I have some ~6 year old Duracell Rechargeable Accu AA and AAA cells. The AA's are 1800 mAh, and still last around a month of decent use in my cordless mouse. I don't mind beating them to death in such a menial applications compared to my nicer cells. When the low battery indicator starts flashing, I simply top off 2 more and switch them out the next day.

Now, what to do with my ~60 ROV Hybrids....

Edit:
Could put those old cells to use in a ROP MagLite or something. Might as well beat them to death in glory.

[wptski]

A while back I discover several brand new packs of MAHA 1.8Ah and 2Ah AAs still in plastic boxes from Thomas Distributing. Some leaked so badly the cases were rusty. I tried every known trick in the book to revive them and nothing worked. What you read about just charging them, they'll be fine is all BS.

MAHA replaced all that I requested but I should have asked for a replacment for all that were under capapity!

[SilverFox]

Hello Bcwang,

The Eneloop and other low self discharge rate cells are too new to know how well they will handle long term storage. I have had some in storage for almost 2 years now and they are still doing fine.

Tom

[TorchBoy]

On the other hand, I have noticed that occasionally a battery manufacturer will comment that cells are good for 2 years, then should be replaced.

You'd be hard pressed to get the (mythical?) thousand cycles like that.

[Jackson]

The Eneloop and other low self discharge rate cells are too new to know how well they will handle long term storage.

I know the Eneloop docs that come with the cells state that they might require charging before use if the manufacturing date indicates the cells are two years old. That's a lot better than those that recommend replacement after two years.