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Full Version: AA NiCad battery cells are now 1100 mAh rated
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I stopped by my local Batteries Plus store today to pick up another supply of AA flat top NiCad battery cells for battery pack rebuilds and noticed that they were marked "1100" instead of the customary "1000". I asked the clerk about this and he confirmed that AA NiCads are now available in an 1100 mAh rating, up 10% from the previous 1000 mAh rating. I can remember not so long ago when they were only rated at 700 mAh, and about 450 mAh in the 1970s when the LED HP models were made. It also seems that the self-discharge rate is lower, so they hold their charge longer when placed in storage. I realize that NiCads don't compare with NiMH cells for mAh rating, but I prefer to use them because the original charging systems were designed for them.

As far as I can see, the only issue with using NiMH cells in place of NiCd in HP calculators is that it will take longer to charge them. HP's charging circuit is little more than a current limiting resistor, so there doesn't appear to be any potential for mischief that wasn't already present with the NiCD cells.

I prefer to charge cells outside the calculator anyhow.

I now use the "low self discharge" NiMH cells. They have lower capacity (2000 mAh, vs. 2500 mAh for the normal NiMH AA cells). The latest Sanyo eneloop AAs take three years to drop to 75% of their original charge, and are rated for 1500 cycles.

As with alkalines, lithium, and NiCd cells, cheap off-brand NiMH usually have far less actual capacity than claimed on the label and package.

you are quite right that in HP calculators a set of Ni-Mh batteries will be a pretty much ok substitute.

the only caveat (in some other applications), is that when charged using any sort of 'smart' charger circuitry that is not designed with Ni-Mh cells in mind, it is likely the charging circuitry will not recognize the 'end of charge' conditions, which are far most subtle with Ni-Mh's than with Nicads.

as a general rule, as long as you don't charge at higher than 1/10th of the rated capacity (1/20th would be preferable), and don't leave the calculator sitting on charge for way TOO long, then all will be well. in other words, a 2000mAh Ni-Mh cell will be perfectly happy being charged at 150mA or so for a not too long time interval (no more than a day perhaps).

btw, Nicads do still have some advantages over Ni-Mh cells in certain quite specific applications. A Nicad can deliver a MUCH higher instantaneous current than a Ni-Mh cell without causing itself internal injury, making Nicads a good choice in applications like battery drills. The environmental concerns of cadmium in the environment, of course, are a whole different matter!

rob :-)

Sanyo has been making the 1100mah KR-1100AAU cell for at least eight years... and others are currently making 1200 mah AA nicds.

Are the 1200 mAh versions available as flat tops?

Edited: 31 Mar 2011, 3:21 p.m.

NiCad cells also have a memory of usage. One engineer bought an HP65 on a project budget and proudly wore it on his belt, and never used it. He came to me in tears, his battery would only last 5 minutes. I asked him what the instructions said to do, "run it flat and recharge it". My 65 batteries gained strength in use and would last 3 hours. Ordinary Nimh cells have a high self discharge rate, I use Sanyo eneloop with a LaCrosse smart charger. I used to have 2 chargers nearly full time just to replenish the self discharge, now I use one charger seldom. Sam

Where has gone the frugality of engineering? 2000 mAH are 2 Ah !

Walter! I'm deeply disappointed! I would have expected this from anyone else, but not you! 2000 mAH of course is 2000 Milliampere-Henry! What kind of unit is that?!

BTW - sure, 2000 mAh = 2 Ah, but would you also recommend to label all 2000 Microfarad capacitors as "2 Millifarad" ?-)

Dieter

Ooops, that quick and dirty post of mine was dirtier than I thought :O

"mAh" is the far more commonly understood unit by the 'general public' these days. for much the same reason LED brightness is often quoted in mcd's (millicandellas): "Brightness at centre of beam measured as 12000 lux at 40cm, or 1,920,000 mcd".

personally, i'd be happier using the 'correct' units, but the 1/1000th unit has crept into folk culture and taken front seat.

The problem is that if you start using Ah instead of mAh, then you have to use decimal values in most cases, such as 1.1mAh or 1.2mAh. It's always been easier for me to grasp whole integer values.

Yes. Here are some bargain cells with tabs if you want to build your own packs: 1200 mah nicd with tabs