Alkaline vs. NiMH (long)

[georc]

Introduction
I always love reading comparison tests about real cars in Car And Driver, at Edmunds.com, and the like. So I figured how about a Bit comparison test that would address a seemingly constantly asked question:

What happens if I use rechargeables?

Or

How do rechargeables compare to alkalines?

Though far from a laboratory situation, I tried to conduct this test as scientifically as readily possible.

The Procedure
To conduct this test, I used one set of new alkaline batteries and one set of new, first-time charged, rechargeables. Some would argue that to get full potential out of rechargeables, I should cycle them through about four or five charges. However the purpose of this little test was to see how the two battery types compare out of the box. Perhaps an evaluation of conditioned rechargeables would be a good topic for future research.

To conduct this test, I used only one car and one transmitter/charger. I first went through 10 runs with the alkalines. Then I did ten runs with the rechargeables. After the Bit would no longer respond to the transmitter, I would charge it. When the charge led on the transmitter went out, I immediately read the voltage of the battery via the charging contacts on the bottom of the car and recorded it.

The Equipment
MicroSizer RX-7 49MHz (yellow) - stock
GB Instruments GDT-11 Digital Multimeter
Duracell Standard AA Size Batteries (2)
Rayovac Rechargeable NiMH AA Size Batteries (2)
Rayovac PS1 Battery Charger

Prior to the series of runs, I found the voltage of each of the alkaline cells to be 1.55V. Each one had 1.44V after the ten runs. After their first charge, the rechargeables each had 1.41V. After the runs, each cell read 1.33V. While the Alkalines had a higher voltage than the rechargeables after the test, they dropped more throughout the series of runs. It should be noted that the alkalines had a higher voltage after the tests than the rechargeables. However, the rechargeables, before the test, had a voltage 17.5% higher than their rating of 1.2V, whereas the alkalines had an initial voltage only 3% higher than their rating (1.5V).

Before running the tests, I allowed the rechargeables to cool to room temperature. The alkalines were, of course, already at room temperature prior to testing as well.

The Results
The results have been summarized in the attached table image. As you can see, the rechargeables actually had a higher average charge. They also displayed a higher minimum and maximum charge, and also seemed to charge to a more consistent voltage. I would have thought that the alkalines, with their higher initial voltage would have produced higher charges than the rechargeables. As the table shows, this is not the case.

In terms of run times, or performance, or range, there was no noticeable difference between the two types of batteries. However this was not the focus of this test. Thus, these aspects were not closely monitored.

Conclusion
It seems that there is nothing to loose by using rechargeable batteries, particularly those like the Rayovac NiMH cells that were evaluated in this test. Although they may not be able to provide as many runs as alkalines on one charge (again, this was not evaluated in this test), they are rechargeable, so in their total life cycle, they will far outlast the disposable cells.

From an environmental standpoint by not using rechargeable cells, you more quickly add toxic material into our landfills. Thus using rechargeables also shows that you have environmental conscience. Furthermore, NiMH rechargeables, when they are through with their effective life cycle can simply be thrown into the normal trash with clear conscience, unlike NiCds.

In the long run, the decision is yours. Spend your money as you please. It seems that the actual performance difference between the two is fairly insignificant, though, in this test, the rechargeables held a slight edge.

Future Research
After conducting this test, I have conceived of several topics for future research:

Run the same test, substituting NiCds for the NiMH cells.
Run the same test, substituting Rayovac’s rechargeable alkalines (yes recheargeable alkalines) for the NiMH cells.
How many runs can the rechargeables produce, on one charge, as compared to alkalines?
Compare the times of runs charged by rechargeables vs. those charged by alkalines.
Run a comprehensive test of charge, quantity of runs, and length of runs utilizing all four cell types.

If anyone feels like jumping in and running any or all of these tests, or a reproduction of the one run above, please do and share the results with us. Knowledge is power.

Thanks for sticking through this long post.

NOTE:
I hold no stake in the battery business – alkaline, rechargeable or otherwise. So I have nothing to gain from promoting one type of cell over the other. This was done simply in pursuit of a quasi-scientific evaluation of the questions posed herein, as well as to further my own knowledge of a hobby that I see quickly bordering on addiction. Does anyone know of any twelve-step programs for micro r/c addiction?

[georc]

Well, for some reason, the attached table isn't showing up.

Here it is in text:
Run Alkaline NiMH
1 1.42 1.43
2 1.43 1.44
3 1.39 1.44
4 1.41 1.44
5 1.38 1.44
6 1.41 1.44
7 1.43 1.45
8 1.43 1.41
9 1.36 1.44
10 1.42 1.43
AVG 1.41 1.44
MAX 1.43 1.41
MIN 1.36 1.45
RANGE 0.07 0.04

[Namuna]

Good stuff georc!

[hogjowlz]

my friend has a battery meter that is hooked up to a pen graph so you can compare two batteries as they drain. he uses it for larger batteries but im sure he could confirm your data or already has. ill have to show him this thread.

A good test would be to measure the voltage of the cells while the Bit is charging. The NiMh cells should show a higher voltage under a heavy load than alkaline batteries. This is why they work so much better in flash cameras, the flash needs a high inrush current to charge the capacitor. This may be the reason why they don't recommend rechargeables for the Bit. The charging current may be too high. The internal resistance of the alkalines may serve as a "regulator' of sorts........

[georc]

The way I understand it, from working with larger scale R/Cs, NiCds can handle charging at a higher current than NiMH cells. To throw another variable in, a test of a NiCd (stock) vs. an NiMH cell in the car would be another intersing future avenue of research to pursue. Given the same rate of charge through their life cycles, I wonder how the two would compare in terms of long-term durability.

[hogjowlz]

nicd should be more durable in the long run. at least from cell phone experience. someone needs to come up with a lithium ion cell that will work with these things.

less weight and size.