Storing NiCAD's & NiMH's

[Dukester]

Storing NiCAD\'s & NiMH\'s

What is the best way to store NiCAD's and NiMH's for prolonged periods, say for 4 - 6 weeks? Should they be fully charged upon putting them on the shelf or should they be fully depleted? Does it even matter?

 

[PeLu]

Re: Storing NiCADs & NiMHs

4 to 6 weeks is not a long time and I actually do not care about them at all for these short period.
After several months you may want to cycle your cells when you use them at higher currents.
I charge them before storage, it may be that I need them earlier as expected.

 

[SilverFox]

Re: Storing NiCADs & NiMHs

Hello Dukester,

If you figure a 1% discharge rate per day, the cells will be down to about 20% capacity in 180 days. I have observed that my cells self discharge rate is less than 1%, but that should give you some indication as to what is happening.

If I were to store cells, I would cycle them every 6 months. I would also expect that it might take a few duty cycles to get them back up to top performance.

Tom

 

[gwbaltzell]

Re: Storing NiCADs & NiMHs

I have to agree 4-6 weeks is not long enough to worry about. 8-12 maybe. I seem to have had better luck with long term storage with them dishcarged, however unless you can get to invidual cells in a battery, I still won't go below 0.8 V per cell. I think Saft used to state something similar, but I no longer find it on thier site.

 

[Muppet]

Re: Storing NiCADs & NiMHs

Battery university recommends 40% charge in a dry refrigerator-temp place.

 

[jayflash]

Re: Storing NiCADs & NiMHs

So the latest info is to NOT store cells that are fully charged? Past recommendations stated to fully charge NiCd cells before storing. Do different chemistries have different storage requirements that you know of? For example, lead/acid batteries should be charged and topped off to prevent plate sulfation.

 

[SilverFox]

Re: Storing NiCADs & NiMHs

Hello Jayflash,

Muppet pointed out the article at Battery University. It lumps Nickle based and Lithium based chemistries together and states that the effects of ageing are minimized when cells are stored at a 40% charge.

http://www.batteryuniversity.com/partone-19.htm

Contrary to that information, I store my LiIon, NiCd and NiMh cells fully charged. I should also point out that my long term storage is along the 3 month time frame. I believe they are talking about storage for a year or more.

Tom

 

[PeLu]

Re: Storing NiCADs & NiMHs

LiIon cells degrade much faster when kept fully charged.

And Battery university does not have a high reputation amongst battery-chemical engineers.
Just offering a lot of data does not make them more accurate.

When I know I do not need a cell/battery for some time, I keep them as cold as possible.

I do have this problem with power packs for rotary hammers for cave rescue. You do not need them for a long time, but then you need them immediatly. Keeping them in a dry freezer at -18°C works for us. Trickle charging was not so good.

 

[Steve K]

Re: Storing NiCADs & NiMHs

About 10 years ago, I worked with a group that built electical power subsystems for satellites. The system used nicads... really big nicads!

When the system was put in storage (prior to delivery to the customer), the batteries were fully discharged by applying a low resistance load to each cell. Once it was fully discharged, each cell was shorted out. After this, it was stored in a large refrigerated room.

I'm not sure why the cells were all discharged. Maybe to prevent crystalline growths in the cell? Maybe just to avoid a safety issue? (a fully charged battery can be a safety hazard if accidentally shorted).

Steve K.

 

[PeLu]

Re: Storing NiCADs & NiMHs

When I got SubC Nicads in the seventies, they came with the instructions to store them empty and they stated the reason is that many shortages occur while storing the batteries (not only single cells).
My personal theory is to keep them as cold as possible without freezing the electrolyte.