Features October 15, 1998 Issue

Alkaline Battery Tests:
Results Say It's Bedtime For Bunny

Despite the memorable ad campaign, Energizer ran a distant third behind Duracell in all but our 6V lantern battery test. But how's this for a shocker—there's less than meets the eye under the copper top of the Duracell 6V ‘lantern’ battery.

The last time we tested alkaline batteries (June 15 and November 15, 1995), we reported that Duracell dominated the market, with Energizer and Rayovac a distant second and third, followed by the unadvertised generics. Although that position has not changed much, we now learn that 75% of battery sales are in the AA/AAA families that power everything from electronics to toys.

We also assumed last time that D cell performance should reflect the performance of any size battery made by a given manufacturer. This time, we tested all three sizes to see if that is the case (it isn't). In fact, Duracell told us each size is designed by a different team of personnel.

Lastly, both Energizer and Duracell have installed “gas gauges” on their cells to tell us how good the battery is, so we decided to see how well these devices perform.

How We Tested
Like last time, we configured a simple test fixture comprised of a kitchen quartz clock, a load, and a place to install a battery. Although we’ve been criticized for using this ridiculously simple fixture, it has some definite virtues:

1. Anybody can duplicate our work with a couple of clip leads.
2. Each cell is subjected to the exact same load in any given test. (We varied loads this time to verify performances from moderate to heavy).
3. A quartz clock keeps good time over a wide voltage range until it stops at consistently the same voltage point.

What we did differently this time was to operate the clock on it’s back. Here, the weight leverage was eliminated when the clock attempts to move the hands from 6 hours to 12 hours and this resulted in a more precise measurement of the cut-off voltage. Last time we reported it at 1.1V when it is, in fact, 1.05V. It should be noted, as most who have had any experience with flashlight batteries are aware, that batteries last longer when used intermittently. Our technique of applying a continuous load perhaps shortened the lives of our test batteries, but all were subjected to the exact same conditions.

The result yields an accurate capacity measurement of a 1.5V battery between its start voltage and its “fail” voltage (1.05V). At 1.05V, flashlights are dim (but usable), portable radios are scratchy, portable TVs finicky, and we consider the battery dead. It may run a low-voltage toy for a while but we don’t care. Also, batteries, after a certain amount of rest, seem to be able to rise from the dead temporarily. The second life is usually short—no more than a minute when we tried it—and of no useful significance to the user.

The lantern battery test fixture differs although it still employs the clock. Here, we squeezed them out like a sponge to measure their capacity while we periodically took voltage measurements to gauge their usefulness. (The voltage measurements were used to extrapolate when a battery was at 3V if we were not present to witness the exact time.)

Here’s how it works: First, we measured 750 milliamperes (ma) of lantern current using a halogen bulb to establish our target load. Then we measured a lantern’s current using a standard filament bulb and found it to be 500ma. We configured our test load using the conventional lantern (500ma) plus a parallel bulb that draws 240ma in series with two diodes to simulate our halogen load. The two diodes act as a voltage regulator to establish voltage for the clock (measured at 1.28V start, 1.05V end).

Then we mounted our test configuration in our darkroom and pointed the lantern at a wall 3 feet away. During the first battery test, we took lots of voltage measurements over time until the battery was dead. It was here that we decided the lantern was of little use once the voltage was down to 3V. It could still be used to read a chart and perhaps find something close up, but that was about it. We called the 3V point the end of useful life and we declared the batteries dead when the clock stopped.

What we Found
Initially, our intent was to test both D cells and AA cells using a light bulb load with a 350 milliampere drain and be done with it. A standing rule of thumb for years has said that a AA battery has 1/7th the capacity of a D cell so we intended to record our results and report what we found.

Then we realized that Energizer AAs were not performing as advertised—not even close in fact. Energizer claims its AAs are 15% better than Duracell in some ads, 30% better in other ads. The fine print says results may vary by device. [Duracell says they’re better than Energizer in the devices we use most; Rayovac claims they deliver the same power as everybody else but at a cheaper price.]

We called Energizer to find out what we were doing wrong and were told that our load was too light. Anything over 500 milliamperes, we were told, and Energizer wins. We asked about 750 ma. They said great. They said we should even try 1,000ma or perhaps 1500ma. So, we reconfigured our test load to use resistors instead of a light bulb and off we went to purchase another bucket of batteries.

First, the reader must be aware of the fact that a 350ma, 750ma or 1500ma load is not what it seems. Because Ohm’s law says amps = volts/resistance, the current only holds true if the voltage stays at 1.5V, which it does not. Initially, each battery under test drops off in voltage at turn-on because of it’s internal resistance. Then the voltage falls off further as the battery is drained. The typical D cell started at 1.45V or so and the typical AA cell at 1.4V at 350ma load. These voltages were lower at the outset with a higher current load, and no AA battery would support a voltage high enough to drive the clock at 1500ma.

It should be said that our 350ma drain more closely approximates a typical load you might find in the real world. A handheld GPS, for example, will draw between 150ma and 250ma, making a load of 350ma a severe but not unreasonable test for AA batteries. D cells are much more likely to be used for products such as flashlights, which draw two to three times as much current. It should be remembered that the nominal voltage rating of any of these single-cell batteries is the same (1.5 volts) regardless of battery size; capacity and current ratings go up with physical dimensions.

In summary, we found the following:

1. D cells at 350ma: Duracell and Rayovac first in a dead heat, with Energizer behind Radio Shack (a generic). In fact, Walgreen and Eckerd generics compare well with Energizer here.
2. D cells at 750ma: Duracell wins, with Rayovac second and Energizer third. Radio Shack had one good performer and one very poor.
3. D cells at 1500ma: Duracell first. Rayovac has a higher average for second. Energizer had one good and one bad for third, and Radio Shack bombed with one complete failure for last.
4. AA cells at 350ma: We’d call Duracell and Radio Shack even followed by Energizer. Rayovac compares here with the generics from Walgreen.
5. AA cells at 750ma: Rayovac nosed out Duracell slightly, followed by Radio Shack and Energizer. The useful time here is short—25 to 35 minutes or so.

The AA cells were not tested at 1500ma because they cannot sustain a voltage over 1.05V at this load.

For our results, we averaged the useful life spans of four batteries for the sake of a quick comparison. As any frustrated battery buyer knows, batteries vary greatly right out of the pack, some lasting seemingly forever, others virtually dead at the onset. In terms of hours, the Duracell and Rayovac D cells, at 750ma draw, averaged a bit over 6 hours (a Duracell had the single longest life at 7 hours, 50 minutes). Radio Shack and Energizer were a virtual tie for worst average—4 hours, 48 minutes and 4 hours 51 minutes, respectively. Although we dutifully tested the D cells at 350ma and 1500ma, we haven’t included the actual time results because they really do not reflect real-world use.

With the AA cell batteries (see chart, page 5), Duracell again lasted the longest at 350ma, with an average of 4 hours, 18 minutes. Radio Shack, this time, was close behind at 4 hours, 15 minutes. Energizer was a distant third at 3 hours, 24 minutes, with the Albertson and Eckerd generics bringing up the rear at 2 hours, 18 minutes and 2 hours, 6 minutes, respectively. The higher amperage test (750ma) turned out to be fairly meaningless for AA cells, with no batteries lasting an hour (Duracell led with an average of 30 minutes, and Energizer was last).

The Gauges
The “gas gauges” provided by Duracell and Energizer differ dramatically. Duracell provides a thermometer-like device with a red/green band. It is activated by depressing a button on each end of the battery and the band activates completely up the green portion on a new battery. When the battery is discharged to 1.05V, the red band activates up to but stops right at the green, which indicates a border-line dead condition.

The Energizer gauge employs a liquid crystal-like “GOOD” indicator that is activated similarly by depressing buttons on either end of the battery. On a new battery, this display is crisp and “GOOD” stands out clearly. Discharged to 1.05V, it still says “GOOD” but not quite as crisply. Unfortunately, the novice would have to gain experience distinguishing between a good and bad battery to recognize that a dim “GOOD” really means not so good.

We vote for the Duracell display hands down.

Lantern Battery Results
We tested only Duracell and Energizer alkaline batteries in the 6V test because they were the only ones locally available. We did find Rayovac carbon zinc-based units (we couldn’t find any alkaline units) for comparison. Incidentally, whatever the make, if it doesn’t say “alkaline” on the label, chances are it’s a shorter-lived carbon zinc, "Heavy Duty" or not.

Here, the Energizer is the winner by a large margin, providing more than three times the life of the standard (cheap) units and Duracell giving us a bit more than twice the life of the no-names.

Then we wondered why. The Energizer lantern batteries are noticeably heavier (2+ pounds, compared to 1 pound, 6 ounces for the Duracell). The Duracell units were not only lighter but they seemed hollow and tinny to the tap as though there wasn’t much battery inside.

Turns out, there wasn’t. To our dismay, we found four standard Duracell alkaline D cells (labels and all) stacked serially inside with a cardboard filler. For double the price (in some cases), you get the box that gives it a lantern battery shape.

We opened the Energizer unit and found it contained four unique 1.5V cells, connected serially, each nearly 50% longer than the standard D cell. The life test graphs nearly correspond with the volume comparison, with the Energizer batteries averaging a life (before reaching 3V) of about 27 hours compared to about 16 hours for the Duracells.

Greater volume means greater capacity, which, in turn, means that a battery can handle greater drain at a given voltage and last longer.As we've already noted, not all 1.5V cells are equal, except in terms of no-load voltage.

Granted, Duracell's alkaline technology outperforms the old carbon zinc cells, which are still being sold. Nevertheless, we are disappointed with Duracell, which obviously has the capability of giving us a better product—instead of selling us four D-cells packaged to equal 6 volts. We asked Duracell several times for an explanation but got none.

What All This Means
Regarding AA and D cells: To the mariner with his flashlight and portable electronics, the top one-third of a battery’s voltage is what counts. Typically, a battery-operated electronic product has an operating power supply range of 25%. That is to say, a 12V device with eight cells in series will operate satisfactorily between 9V and 12V. A 6V device with four cells in series is alright between 4.5V and 6V. We tested batteries to a 33% reduction in voltage.

Does this mean Energizer is being less than candid? Not necessarily. Because the biggest market today is AA/AAA batteries, it turns out the major buyers are mothers who plug these things into toys. Could be Energizer might win going away in the lower two-thirds of a battery’s capacity. All it does is drive a little motor that often runs at ridiculously low voltages. So what if the bunny beats his drum slower than the average heart in a geriatrics ward? It looks good on TV.

The boat owner who is depending upon a handheld GPS or VHF can be said to be marching to a different drummer. His interest is in how long his electronics can operate reliably. We feel that his interest is best served by ignoring the length of time a battery can supply current at a voltage less than 75% of what it's rated for.

Regarding lantern batteries: Clearly, Energizer designed a unit intended to give long life to a 6V lantern. We’ve not seen lantern batteries employed in any electronic devices, and even we were satisfied that discharge to 50% voltage was still usable for powering a light.

Conclusions/Recommendations
Of the popular name-brand batteries, Duracell generally remains the leader in performance in both the D and AA/AAA cell families and we see Rayovac as a very close competitor, with Energizer not too far behind. This is the voltage range we are most interested in, and we couldn’t care less about the energy capacities below 1V for a single cell.

Price is a separate issue. Among the generics included in our tests, Radio Shack did well but they are priced high, even when compared to the name brand units.

Typically, name brand units of two-pack D cells sell for $2.50 plus or minus 20¢. Generics vary from $1.98 to $2.50. Four-pack name brands of AA cells are $3 plus or minus 25¢; generics are from $2.25 to $3. Lantern batteries are expensive with prices ranging from $6 to $10. Clearly, the price shopper needs to do his own digging since so much depends on the whims of the store.

We think reliability and performance count more than price, at least in critical applications. Our choice at this writing, except for its dubious lantern batteries, continues to be Duracell for most applications.

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