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Author Topic: Comparing AA cells' mAh's: Alkaline vs NiMH, etc.  (Read 8274 times)
VK5CQ
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« on: March 16, 2010, 04:16:43 AM »

Have you ever wondered why there are no "mAH" ratings on Alkaline cells?

I like to compare capacities of cells before buying; it's been easy with NiMH cells, I've seen them up to ~2700 mAh (for AA's)

But how do Alkaline AA's compare.

Wikipedia leads me to believe that it's not so easy to compare (ie, from what I knew of them, before today; and - even with what I've just learned from a quick on-line search - I'm still a bit puzzled...).

Here's what one article says of Alkaline cells:

"The capacity of an alkaline battery is strongly dependent on the load.

 An AA-sized alkaline battery might have an effective capacity of 3000 mAh at low power, but at a load of 1000 mA, which is common for digital cameras, the capacity could be as little as 700 mAh.

 The voltage of the battery declines steadily during use, so the total usable capacity depends on the cut-off voltage of the application."

...from: http://en.wikipedia.org/wiki/Alkaline_battery

So, I think we need to know the "cut-off voltage(s)" of
all the hand-held radios we can run from AA-cells, etc.

Any thoughts?

(I guess the best way to test is to run timed tests,
but - with so many battery brands & models, that's a lot of work!)

PS Anybody know the CoV's for Yaesu's line of VX's, ie, VX-8R, VX-7R, etc.?

(Each has a [rather costly] battery case available for it, and I'd like to compare run-times - even for receive-only applications - of each one, with the best AA-cells that work in each of them.)

If you have such a radio, perhaps you can find & post its Cut-Off Voltage, in a quick reply...

TIA
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AA4PB
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« Reply #1 on: March 16, 2010, 05:29:42 AM »

Most major manufacturers have capacity specs on their alkaline cells. Its no different than any other cell except that the variables are much larger. The mAH spec on any cell is to a specified cut-off voltage, at a specified load current, and at a specified temperature. Change any of those variables and the capacity changes. The amount of impact those variable have on capacity varies with the type of cell. Alkalines change more than NiMH and many others but not as much as good old lead-acid.

The bottom line is that its pretty difficult to tell *exactly* how long any battery type will function in a given application using only the rated capacity without testing.
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K2DC
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« Reply #2 on: March 16, 2010, 05:46:34 AM »

To add to AA4PB's comment, it's my understanding that the only difference between a 700 mAh alkaline and an 1800 mAh alkaline is the test results.  I have been told that there are no differences in the materials or the manufacturing processes.  All of the cells are tested, and the higher capacity ones are set aside, labelled as "high capacity" and sold for a higher price.  You don't make 1800 mAh alkaline cells - you find them.   They simply cherry-pick.

73,

Don, K2DC
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NR4C
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« Reply #3 on: March 16, 2010, 05:51:02 AM »

This may not be the answer you want, but here goes.  In my use of several HT's, and other electronic items, a set of fresh "AA" Alkaline such as "CopperTops" will outlast the charge on an same size NiMH or NICAD battery.  However, you can recharge the NICAD or NiMH and go again. And, you can pick up "AA" Alkalines just about anywhere they sell batteries.

mAH capacity ratings are only so useful as they are dependant on a lot of variables.  you will only get the given capacity at the tested discharge rate from a fresh charge down to a fixed cutoff voltage.

Good luck...

...bc  nr4c
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N4NYY
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« Reply #4 on: March 16, 2010, 05:57:07 AM »

NIMH ability to store a charge, and hold it, really sucks. You have to charge an NIMH and put it to use almost immediately. Nowhere is this most evident as when you use a digital camera or power tool, that you charge fully 3 weeks ago, and the batteries die almost immediately.
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K5LXP
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« Reply #5 on: March 16, 2010, 06:08:00 AM »

AA4PB's comments are spot on, and I would add that unless you buy a "name brand" alkaline, your results can be highly variable.  I have a West Mountain Radio battery analyzer and whenever I find a "deal" on alkalines I'll buy a pack and run a profile to see how they compare to the name brand ones.  Often the difference is only a few percent and therefore they really are a good deal, other times they're truly awful, with the typical issue being high internal impedance.  I've seen the same with bargain NiMH batteries as well, so I never trust what's marked on the cell.  There are deals out there on batteries but you really need to test a given set to really know what you're getting (with the bargain/no-name brands).


Mark K5LXP
Albuquerque, NM
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KB1LKR
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Posts: 1898




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« Reply #6 on: March 16, 2010, 06:10:04 AM »

It is also worthy to note that NiMH's (particularly the new lower self discharge versions), and NiCd's, have lower internal impedance than alkalines, so the NiMHH's will outperform an equally rated alkalines (and low self discharge NiMH's discharge may outperform slightly higher capacity regular NiMH's) in high peak discharge applications, e.g. HT's, large camera flashes (they recharge the flash capaciter faster too) & digital cameras.

NiCd's have historically had the lowest internal impedances, hence their popularity in cordless power tool batteries long after NiMH had taken over elsewhere.

For low peak current applications or where shelf life is important (scanners, flashlights, TV remotes and *especially* smoke alarms), alkalines remain the battery of choice.
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VK5CQ
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« Reply #7 on: March 16, 2010, 06:42:33 AM »

The VX-8R's manual (Thanks, Mods.DK!) says that ONLY Alkaline AA's will do, in Yaesu's (optional) 3-cell holder.

Some radios work fine with NiMH cells in their holders.

What do we know about various radios' cut-off voltages...

...that might explain Yaesu's insistence on alkaline's and some radio's (& GPS's turning off sooner than expected?
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NR4C
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Posts: 312




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« Reply #8 on: March 16, 2010, 09:48:47 AM »

Don't forget that Alkaline cells are nominal 1.5volts, while NiCAD and NiMH cells are nominally 1.2 volts.  Soooooo, 3 Alkys will provide 4.5 volts, while the rechargables are only 3.6 volts.  Now, the LI-Poly used in the Yeasu pack is nominal 3.7 volts, so there is the problem.  you'd need to use more cells with the rechargable "AA"s, but the 4.8 volts would likely fry something.  You're not gonna be happy with any other than "AA" Alkaline cells I'm afraid.

...bc    nr4c
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WB6BYU
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« Reply #9 on: March 16, 2010, 09:50:01 AM »

Alkaline cells are typically 1.5V when new, while rechargables such as NiMH and NiCads
quickly drop to about 1.2V.  If the radio requires 4 volts to run, three Alkalines will last
much longer than the rechargeable cells to that point.  But if the cutoff voltage is 3.5V
the opposite may be true.  Alkaline cells have a higher internal resistance, so can't
deliver as much current:  with my TR-2600 HT I can only get 1 watt output from 6
Alkaline AA cells (9V), but the rechargeable battery pack (7 cells = 8.4V) gives me
2 watts output.  For extended use I always carry Alkalines

Charge capacity ratings are available for most commercial Alkaline batteries, either on
the manufacturer's web site or (to find a number of them in one place) at www.mouser.com,
who has a convenient table to compare the rated capacity of the various batteries they
sell.  Typical capacity for good AA Alkaline cells is around 2Ah (2000mAh).

Actually, for maximum performance at minimum weight, I'd choose the lithium AA cells,
though they are considerably more expensive.

Here is an interesting comparison of the operating life of various batteries as measured
over time, load, temperature, etc.

http://www.foxhunt.com.au/misc/batteries/aa_batteries.pdf
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AD5PE
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Posts: 66




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« Reply #10 on: March 16, 2010, 06:31:19 PM »

Bottom line when comparing battery chemistry and construction is their internal resistance and impedance.  Some types are designed to deliver a large current for a short period of time (or in short bursts) while others are designed for a slow steady draw.  Also, all batteries will "self discharge" when not in use, but that rate also varies.

The alkaline battery has a very slow self discharge, so good the "flashlight in the glovebox".

It also has the most internal resistance, so it's good for long operation at low current/intermittent use (TV remote, AM receiver or scanner).  It might be rated 2000mAh but that is 20 hours at 100mA.  Think deep cycle trolling motor battery.

The NiCd has the best ability to deliver high current.  So a 2000mAh NiCd (if such a thing exists) might actually be rated at 2 hours at 1A.  It might or might not run a scanner for 20 hours assuming a 100mA draw - in my scanner, the lower "starting point" (1.2 vs 1.5V nominal) means 14 or 15 hours is more typical.  But it's the way to go for that cordless screwdriver!  The high current burst equates more to the normal car lead acid battery (high current all at once).

NiMH is the "RV" battery - some "cranking" ability (better than alkalines), but better "deep cycle" and "shelf-life" than the NiCd.

Li and Li-Ion are a whole different animal.  The primary driver on Li based batteries is lighter weight, but they also can obviously provide high current in bursts, as many HTs come with Li based batteries.  Also, I've found the Li based AA disposables (Energizer E2 (e squared) and equivalent) to be very effective in digital cameras and flashes.  They'd probably be the best disposable (as in non-rechargable) choice for backup HT batteries since they're also 1.5V
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