NiMH Batteries: Long-Term Storage ?

I accidentally wound up with an extra set of NiMH batteries and it's going to be quite a long time before the first set goes South and I need the second - as in 1-2 years at least.

How would you store that extra set so as to maximize it's life/availablity?

Fully-charged ?

As they came in the box ?

Something else ?....

Or just bite the bullet and figure on them not surviving that long on the shelf ?

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Pete Cresswell
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(PeteCresswell)
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How about swapping them out in the device every couple months? That might preserve them. I think if one is just left sitting, it will go bad.

Jon

Reply to
Jon Elson

See section 3.2 on Pg 4:

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Jeff Liebermann     jeffl@cruzio.com 
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Jeff Liebermann

Per Jeff Liebermann:

Now *That* is a battery manual....

Thanks.

"When charging for the first time after long-term storage, deactivation of reactants may lead to increased battery voltage and decreased battery capacity. Restore such batteries to original performance by repeating several cycles of charging and discharging."

I guess that explains the "Refresh" button on the SunLabz charger I got for these things.

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Pete Cresswell
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(PeteCresswell)

It's a rather odd way to describe a unique NiMH phenonmenon. A brand new battery will NOT deliver the full rated capacity until after it has been charge/discharge cycled a few times. I've been told that this is also a problem if a used battery has been stored for some unspecified time.

I attempted to test for this at: Note the increase in capacity after each run. I didn't bother checking how many charge/discharge cycles were needed to bring it to full capacity, but my astute guess(tm) is 3 or 4. I also haven't bothered to research the chemistry behind the phenomenon. I probably should also test some LSD (low self discharge) NiMH batteries, such as Eneloop. I also should get off the computah and do something useful.

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Jeff Liebermann     jeffl@cruzio.com 
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Jeff Liebermann

Per Jeff Liebermann:

I only read about Eneloop after I had ordered these things.

Something like a factor of six or something improvement in self-discharge..... and I wish I had known beforehand....

Self-discharge seems like the major drawback to NiMH: you need it, you haven't used it for awhile, and it's not there when you need it.

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Pete Cresswell
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(PeteCresswell)

I noted a similar phenomenon with the Eneloop (and similar) low-self- discharge NiMH cells I've bought. They do benefit from a few full charge-discharge cycles if they've been sitting around for a year or so without use.

Yeah, it makes a big difference for "standby" applications.

There's a tradeoff. The low-self-discharge NiMH cells have a lower capacity than "standard" ones of the same form-factor. I've seen differences of 20-25% in practice. For high-quality AA cells, the low-self-discharge ones I've bought tend to top out at around 2000 mAh, while "standard" versions from the same manufacturer run up to 2400-2500 or so.

So, if you tend to charge your NiMH cells and then use them immediately (e.g. taking lots of photographs while on a trip) standard cells are the way to go. For "standby" applications, low-self- discharge cells work out better.

Reply to
Dave Platt

That's what I do with the AA batteries (ENELOOPs) I use in several cameras. Each camera uses 2 of'em, and I mark pairs of batteries with unique colored bands of magic markers (sharpies). I keep the pairs together -- in the cameras, during charging, in storage. I regularly rotate the sets via recharging.

Jonesy

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Reply to
Allodoxaphobia

As someone else suggested - rotate them in use.

Nickel batteries thrive on use, it was certainly the case with cadmium - probably less so with Mh.

Even the allegedly low self discharge types self discharge, so they'll end up flat in storage wherever they start off from, I have a suspicion that stored fully charged may be more prone to whisker shorts.

A while back, the Lidl discount store had "ready to use" Ni-Mh cells, so I bought a load. A pair of cells fresh out of the charger for my camera, lasted just long enough to charge the flash - then the camera shut down with low battery warning. Rotating the cells through other uses has improved their performance.

Reply to
Ian Field

Per Dave Platt:

I guess the truly-obsessive could look at a chart of the self-discharge, note where 20-25% happens, and then choose one or the other type battery based on one's expectation of how long they will sit before use.

viz:

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Looks like the crossover point happens after about 20 days and the regular ones need re-charging on a monthly basis to assure 50% capacity when needed.

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Pete Cresswell
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(PeteCresswell)

Nickel chemistry might be on the way out, precisely because of self discharge.

An ever increasing number of cordless devices are appearing on the market with lithium instead of nickel.

Reply to
Ian Field

Yep, and there's a problem. If you charge to 100% and leave it there, the LiIon battery slowly deteriorates. See Fig 5 at: That's one reason you don't see any LiIon UPS/SPS battery backup power system. There are plenty of retrofit kits and replacement batteries, but nothing from the OEM's. Same with cordless phones, electric shavers, and other devices that run permanently on chargers. About the only way to do it is to use a battery that's about twice the calculated capacity ma-hr, and only charge it to 50% of capacity.

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Jeff Liebermann     jeffl@cruzio.com 
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Jeff Liebermann

Yup. The two classical Li-Ion deterioration factors are temp and SOC

- in each case, the higher it is the higher the deterioration.

When we were doing Li-Ion capacity/cycling testing (in association with charger design) we tried moving from the cell manufacturer's "specified terminating voltage for full spec capacity" (4v20) to 4v10.

We found that we were achieving between 85% and 90% of the 4v20 capacity. We didn't have enough lifetime to waste doing deterioration testing for 4v10, but I'm sure that the average always-plugged-in laptop would get double the battery lifetime (cycles, years) at 4v10 terminating voltage with only that commensurate loss of run time.

It's a pity manufacturers of laptops, smartphones etc are obsessed with maximising run-time as a selling spec.

Reply to
pedro

Well...offer a laptop with less battery life than the competition and see what happens to your market share. It's not manufacturers, it's customers who are obsessed with run-time. If you're gonna get a new smartphone every two years, do you really want to trade run-time for a battery that lasts 10 years instead of three?

What would be interesting is a customer available parameter that traded battery life for run-time.

So, what was the termination voltage in your final charger design?

Reply to
mike

The critical terminal voltage isn't necessarily a constant.

ISTR: earlier generations of cells requiring 4.10V, most current types like

4.20V - I recently encountered a cell type that should be charged to 4.30V. The graph on the datasheet indicates useable capacity takes quite a hit if you only charge it to 4.20V.
Reply to
Ian Field

The current "solution" is for laptops to offer a mode where it charges to about 50% of capacity for those that use laptop as a desktop replacement, where it is plugged into a charger 100% of the time. If you want to go somewhere, you're expected to change the setting and quickly charge the battery to 100%. Of course, the setting is buried under several layers of menus in an obscure utility only accessible if you know the cryptic name and obscure location. I also note that this feature seems to be more common on laptops with non-replaceable batteries (Aerobooks and Ultrabooks).

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Jeff Liebermann     jeffl@cruzio.com 
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Reply to
Jeff Liebermann

Maybe I should have said manufacturers were obsessed with remaining competitive ...

Jumper-selectable 4v10 and 4v20 (solder-blob bridge on the PCB - the design was for a large battery supply house). That way the vendor could tailor it to the customer application - which was NOT commodity appliances.

Reply to
pedro

Predictably ...

Yep, the rest go with the full SOC, give you the big run-time spec, and sell you replacements (batteries, or - more often- machines).

Reply to
pedro

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