Sanyo Eneloop batteries and charger: Work for Texas Instruments 84 calc?

batteries,

But why would you expect _any_ rechargeable battery (regardless of chemistry) to keep its charge for several months?

I think there are two effects here - how much of the energy going into the battery is being lost as heat, and how much of an effect the heat change has on the voltage. NiMH cells differ from NiCd in both respects.

That does seem to be the case. It appears that there are a couple of ways to charge NiMH cells fairly safely:

[1] At a nice, slow rate - .1C or even a bit lower. At this low rate, the cells don't heat up very much at all, and thus don't exhibit the zero-delta-V or negative-delta-V full-charge signature. For that reason, neither a voltage- or temperature-sensing approach can be used reliably, and a timed charge shutoff is the only alternative. [3] Use a relatively fast charge rate - no less than .3C, with .5C or even 1C being common. The cells do warm up significantly during the fast-charging, and then their temperature starts to rise sharply (and the voltage reaches zero-delta-V and starts down into negative-delta-V) at full charge. Today's fast chargers seem to use either T or delta-T as the primary shutoff indicator, with delta-V as a secondary, and a timed shutoff as the final failsafe. Early versions of the Maha/Powerex MH-9000 had a reputation for occasional shutoff failure - they would not detect full charge reliably, and the batteries would become quite hot as they cooked away. Powerex revised the charger - I think they tweaked the firmware logic having to do with the shutoff detection - and I understand that they *raised* the minimum recommended fast-charge rate from 0.3C to 0.5C. Presumably this results in a more rapid temperature rise at full-charge, and makes it easier to detect.

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Dave Platt                                    AE6EO
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MAHA told me they've never revised the firmware (which I doubt). I've had no termination-failure problems, even at 0.1C.

Ummm... because [1] that's what I need that particular set of batteries to do, in order to do my job, and [2] because that's what the manufacturers are able to make them do, and advertise them to do?

Certainly, rechargeables are not likely to have the charge storage lifetime of primary cells. However, NiCd batteries did/do have a storage lifetime which makes it reasonable to use them for many standby applications, and they have been used that way. First-generation NiMH batteries were markedly worse than NiCd and weren't suitable... but today's ultra-low-self-discharge NiMH actually do the job quite nicely.

They also seem much less prone than alkalines to leak, if left in the device while it's in storage. My experience is that new (unused) alkalines seem to be quite stable in storage, but once you've used more than a small fraction of their charge you've "started the clock ticking" and they'll self-destruct after a couple of years of storage.

--
Dave Platt                                    AE6EO
Friends of Jade Warrior home page:  http://www.radagast.org/jade-warrior
  I do _not_ wish to receive unsolicited commercial email, and I will
     boycott any company which has the gall to send me such ads!

It's not ME that's expecting that, it's the end users. You can baffle them with technical answers until pigs fly, but they keep doing what WE know doesn't work and complaining anyway.

Management is constantly bringing up having devices with rechargeable batteries in emergency kits, but the only options are to let the idiots break open a kit for a drill and finding a dead battery from self-discharge or cooked to death from being in a charger. I've gone thru this too many times to count on all upper and lower digits, even including that digit in my pants.

The new-tech NiMH batteries will hold up for over three months and still at least do a few radio checks. We put a huge placard in the kit to CHARGE the damned radio overnight after drills, but they just toss them back in the kits and bitch.

Back when you could get mercury-celled primary batteries, we'd put those in the kits, but same idiots would pull them out of the kits for day-to day use "just because we ran out of radios" and run them down and bitch when they wouldn't charge. Same for alkaline primary battery packs....

You can't win.......

I was talking in general terms. Until the Eneloop, I've never heard _any_ manufacturer claim their rechargeable cells would hold a charge for a "long" perioud of time.

Yeah, I have a pile of them too. I just never use regular NiMH since the low discharge ones got so cheap. I can put a pair of low discharge NiMH AA cells in my 2-cell AA flashlight (which might go weeks without use), and it's ready to use when needed. Last had to recharge those batteries months ago. Try *that* with regular NiMH cells. Kodak even sells the low discharge cells in a 4-pack, fully charged and ready to use. Find

*that* with regular NiMH cells? Heck no. My regular NiMH cells are now only used in high-current, heavy use applications - where self discharge isn't an issue. I have six remote control units and a cordless mouse that use low-discharge NiMH batteries. They operate almost as long as alkalines. Try *that* with regular NiMH cells.