Testing Battery Life

[cfelliot]

Being unable to find any good battery life data on the Web, I decided to take the matter into my own hands and test various batteries myself.

I constructed a battery tester using an AA battery holder and a 5 ohm 1/2 watt resistor. This arrangement draws 300 ma @ 1.5V. I then ran each battery until its voltage dropped to 1V. This is a very conservative range. The included chart illustrates the results.

The 3 batteries I have tested so far are all non-rechargeable:

Radio Shack Alkaline – 1629 maH
Duracell Alkaline – 1858 maH
Energizer e2 Lithium – 3100 maH!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!1

Note: maH is calculated from the area under the curve.

I am now going to test a few Metals and see how they do.

 

[Charlie99]

Note: maH is calculated from the area under the curve..

Not quite. As the battery voltage goes down, the current goes down. Digital cameras actually have the opposite voltage-current plot --- as the voltage goes down, the current increases. This is because they draw a constant power.

For better correlation with what you will see in digital cameras, you need to put the resistor on the output of a DC/DC converter that is fed by the battery stack.

Linear Technology and Maxim Integrated Products are typical manufacturers of small DC/DC converter ICs. They have small evaluation kits for some ICs that will have all the components you need.

Charlie Allen

 

[donacheson]

Being unable to find any good battery life data on the Web, I decided to take the matter into my own hands and test various batteries myself.

I constructed a battery tester using an AA battery holder and a 5 ohm 1/2 watt resistor. This arrangement draws 300 ma @ 1.5V. I then ran each battery until its voltage dropped to 1V. This is a very conservative range. The included chart illustrates the results.

The 3 batteries I have tested so far are all non-rechargeable:

Radio Shack Alkaline – 1629 maH
Duracell Alkaline – 1858 maH
Energizer e2 Lithium – 3100 maH!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!1

Note: maH is calculated from the area under the curve.

While I haven't looked for years, the energy capacity in mAh for small batteries was readily available from the manufacturers.

Why are you surprised that the energy capacity (mAh) of lithium batteries is much larger than that of alkalines?


I haven't looked in years, but small battery capacities specified in mAh were readily available from the manufacturers. I assume that's still true.

Why are you surprised that a lithium battery has a much larger energy capacity than an alkaline?


I am now going to test a few Metals and see how they do.

 

[alcina]

FWIW non-rechargeables are next to worthless for digital cameras underwater IMHO.

Spring for the rechargeables - there are excellent prices and you won't find no battery power five minutes into a dive!

 

[cfelliot]

Not quite. As the battery voltage goes down, the current goes down. …….

This was taken into account.
The sample time was 60sec. The current drawn across the resistor for the sample time's average voltage was recalculated for each sample time:

= e/r * t

= (e/5 ohms )* 60s

These values were then added together to reflect the total storage capability of the battery.

Digital cameras actually have the opposite voltage-current plot --- as the voltage goes down, the current increases. This is because they draw a constant power……

Battery manufactures rate their batteries as Current * Time = maH (milliamp hours). If you draw more current the life of the battery is going to decrease, I understand this. I was only attempting to measure the total storage capabilities.

I haven't looked in years, but small battery capacities specified in mAh were readily available from the manufacturers. I assume that's still true.

Why are you surprised that a lithium battery has a much larger energy capacity than an alkaline?

Manufacturers sometimes don’t tell the whole story and I couldn’t find any real technical data to back up some claims. Do you have a link?
Surprised ? Yes, 3100 mAh from a AA sounds pretty good to me.

FWIW non-rechargeables are next to worthless for digital cameras underwater IMHO.

Spring for the rechargeables - there are excellent prices and you won't find no battery power five minutes into a dive!

I wouldn’t consider 3100 mAh worthless! I do have metals for my cameras, but the best I have seen is around 2500 mAh. The point of my exercise is to determine if I can minimize changing batteries regardless of whether they are toss-aways. Why do you say they are of no value?

If anyone would like the raw data PM me.

 

[alcina]

If you find some that work, that is excellent news.

In all the ones I have seen tried the non-rechargeables poop out pretty quickly. I believe that rechargeables are usually better value and usually last longer. YMMV.

 

[Charlie99]

Battery manufactures rate their batteries as Current * Time = maH (milliamp hours). If you draw more current the life of the battery is going to decrease, I understand this. I was only attempting to measure the total storage capabilities.

Yes, of course, area under the curve reflects your recalculation of the current at each sample point.

The capacity of a battery goes down at higher drain rates. If you double the current, the battery life falls more than half. That's why, for most accurate measurement, you want to try and duplicate the actual load conditions for your camera.

You might also think about using watt-hours (total energy) as the figure of merit, rather than ampere-hours. Watt-hours is what translates best to camera operating time.

The low internal impedance of NiMH and NiCd batteries means that their capacity doesn't degrade as fast as alkaline batterys when you increase the load. That's why rechargeables work so well in things like digital cameras.

The internal resistance of a typical alkaline AA goes from less than 1/2 ohm, up to over 1 ohm near the end of life. With the heavy constant power (not constant resistance or constant current) drain of a digital camera, the end of life for a alkaline cell will be much higher than 1V open circuit.

A lot of this sort of data is already online, such as for the Duracell AA battery. The most useful graph is the one at the bottom, "Service Hours vs. Power Drain".

 

[cfelliot]

Thanks for the link Charlie!
Interesting!

You’ve given me something to think on for a bit. If the results are load dependant, what would be a good current draw model to use for a test?

What about the characteristics of the lithium battery?

 

[Charlie99]

If the results are load dependant, what would be a good current draw model to use for a test?

The power drain fluctuates dramatically according to what is going on in the camera (processing data, autofocussing, storing data, or just showing something on display).

I'd just take the approximate observed battery life with known batteries and work backwards from there to get an assumed average power drain or current drain. Then use that same power or current level for comparison between batteries.

Charlie Allen

 

[sniffette]

From a non-technical but highly practical point of view... I've found that with any brand of alkaline battery, I have to change my camera batteries after every single dive, otherwise the camera will surely conk out halfway through the second dive, invariably right when I see a really cool fish. Using the energizer lithium batteries, I can easily make it through two dives, and if they are relatively short, three dives with full camera power.

Of course, I hate throwing away partially used batteries, so always end up coming back from vacation with a baggie full of half dead AAs.