Josh Glover wrote:
>> Thanks for the useful information. I've personally started using Sanyo
> Eneloop batteries, due to the fact that they hold a charge for a long
> time on the shelf. Using Wikipedia, I discovered that they are:
>>http://en.wikipedia.org/wiki/Low_self-discharge_NiMH_battery>> Does the wiki seem accurate to you?
>>Unfortunately the only spec quoted on AA cells (and only on NiCd or
NiMH) is mAH capacity. Since this is influenced by temperature, the
discharge rate and the number of cycles already done and varies from
sample to sample, it is not every accurate.
Some 2200mA parts indeed do have have a higher capacity than some 2500
or 2700 parts. Very high figures from people you never heard of are
Since this is not policed not standardised, it's even less useful than
FLOPS or BogoMIPS in Linux benchmarks.
I have found huge differences in self discharge rate with the highest
"quoted" capacity AA being the worst. Some "own brand" Aldi were the
best I've used.
Sanyo are a long time major battery maker and innovator at the forefront
of cheap NiCds in the 1970s and a leading Lithium maker along with Sony.
It seems believable that some Sony batteries are really Sanyo.
"Low self-discharge NiMH batteries typically have a significantly lower
internal resistance than traditional NiMH batteries"
is a suspicious statement. Some high current duty NiMH, Zinc Carbon and
Alkaline claim better performance on heavy current and more "equivalent"
capacity by having conductive particles in the electrodes and
electrolyte to lower cell resistance. This lowers shelf life
dramatically on the primary cells and increases self discharge.
"Sanyo's eneloop batteries are one brand of low self-discharge NiMH
battery, rated at capacities of 800 mAh for AAA, 2000 mAh for AA,
3000 mAh for C, and 5700 mAh for D batteries"
Most C and D cells sold, based on weight and capacity seem to be AA
cells in a big box. Again the Aldi C cells are "real" C cells, with
close to the capacity of NiCd "D" cells.
The Eneloop AA is quoted 2000mA, compared with 1800mA for original NiMH
and 2200, 2500 & 2700 quoted for various AA cell products today.
My experience of testing and that of other published tests is that the
highest capacity is probably fantasy. With the high self dishcharge of
2500mA, a 2000mA battery could in reality give better operation time.
Assuming the 2500mA is real.
Given the background of Sanyo and general published information on NiMH,
the broad sweep of the article seems reasonable. I have no way of
verifying all the details.
It's well established that the capacity of NiMH AA cells is 1400mA to
2700mA and that higher capacity is linked to high self discharge.
NiCd AA was originally 450mA (1975) and increased to about 500mA.
The four pack of Aldi AA NiMH batteries is under 4.70 Eur and work very
well. The Eneloop are about 10 Eur on Amazon and certainly you can pay
more than that in the High Street for dubious batteries.
For my custom Linux PDA I built I used however 2x LiPoly 2200mA
iPod (Classic?) replacement flat packs that fitted on bottom of case.
While no more capacity than 4 x AA cell, and not a huge space saving, it
fitted the form factor better. I had to add a thin plastic sheet as PCB
pins pierced cells on my 1st prototype.
My Military 2 way radio is supposed to use 19 or 20 D size NiCd. 2 x
12V 7.2A Lead Acid Gel cell is much better operation time but two heavy,
so I have replaced battery pack with 18 x C size NiMH. I find that some
brands of NiMH have slightly higher terminal voltage. Other handheld
radio that uses 8 x NiCd AA cell has a "dummy" cell when you use 7 x
Akaline as 8x Alkaline when new is 8 x1.59 = 12.72 and 8 x NiCd fully
charged is 8 x 1.22 = 9.76V quickly dropping to 9V. NiMH is about 1.25V
fully charged = 10V peak.
I have a Linksys WRT54G3G (with OpenWRT/Linux) and 8 x AA size NiMH from
Aldi stay charged over a month and give nearly 4hrs operation. I glue
gunned them inside with a trickle constant current charger. The Router
is a nominal 12V but tests showed it was reliable down to 9V, so the
8 x NiMH is a good choice and 8 x NiCd would be a bit low. Stick it in
your packpack and you have a Mobile WiFI hotspot for your Gadgets
assuming you have a Mobile Modem connected. A USB 2.0 PCMCIA adaptor works.
I've also run Wrap1E board off NiMH and used C program on Linux
controlling the GPIO pins for a Turbo charge. The HW interface is
designed that if the SW is not running you only get a safe trickle
charge. Exploding AA cells are alarming.
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