Introduction

Anyone who gets a digital camera quickly develops an interest in batteries as well, because these things are so power hungry! Except for those that use proprietary battery packs, the usual format is the "AA" size, and the most common solution is NiMH cells. There are a number of pages that go over battery care and information. This page documents my own notes and experiences.

This page is part of my set on Digital Photography and Scanning.

Which Brand is Best?

I'd bought several sets of MAHAcells, because they are popular and relatively inexpensive and well-hyped at being the best. I had also picked up a set of DigiPower at the local store, and a set of Kodak had come with the camera.

When I went to order some more on line, I saw that MAHA had a new line, POWEREX, out. It was rated at 1600 mAh, compared to the MAHAcell's 1550. Not much of an improvement, is it? But the price is 73% higher, nearly double! I also read at this time that Sanyo's industrial batteries are "the best" as well. So I ordered a set of each and will test them before buying a larger supply. Meanwhile, I started testing what I have on hand already. My results are surprising.

I've also seen Energizer brand in the stores. Their rating is only 1200 mAh and they are more expensive than buying these other brands mail order, so I have no intention of buying any to try. I also noticed that their C and D sizes are both labeled at 2200 mAh, which is rather odd. Why would the D be no higher capacity than the C? And this is only fractionally higher than other brand's AA rating. The MAHAcell D is rated at 8000 mAh. So why would anybody want these wimpy things? I wonder if they sell poor quality rechargeables in stores so people won't like them, and will keep buying disposables instead?

The Tests

I devised two tests. The first is to run them in a simple resistive load, and measure the voltage periodically. This will give me the decay curve, and also allow me to compute the actual mAh capacity. My apparatus is a flash light that is not the usual tube style, but flat. With the panel removed, it provides easy access to the contacts to measure with a volt meter without removing the cells. The load is 1.4 ohms, but this does not consider the internal resistance of the batteries themselves. Until I replace the fuse in my meter and measure the current drawn directly, I can't state the true mAh capacity.

The second test is more realistic, using the kind of demanding high-current load encountered in actual use. In fact, I used a Vivitar 283 flash unit, and counted how many flashes I could get at full power. The normal recycle rate is 6 or 7 seconds. Once it gets higher than 8, it starts slowing down rapidly. This is my first measurement. It can still deliver more flashes, though, and my second measurement is where the cycle time gets much, much slower at every flash. I also defined a third point at where the cycle time is 1 minute, but decided not to get that last flash or two out as this might over drain the batteries.

The Results

Flash Test

Battery Set rating A B
MAHAcell 1 1550 135 135
DigiPower not given 150 166
MAHAcell 2 1550 170 175
Kodak 1600 210 232

The first set of MAHAcells tested showed the following voltages at the end of the test: 1.13, 1.16, 1.15, 1.03. I wonder if the 4th cell died earlier than the others, and this brings down the usefulness of the entire set? This would also explain why the failure to charge the flash was especially sudden.

The well-respected MAHAcells did very poor. I wonder if set 1 is damaged, and set 2 doesn't keep up with the Kodak. Since all the batteries are the same age and have been used in the same devices, this indicates that they may be more suseptable to this or are poorly made in the first place. Add to this the fact that one set of MAHAcells I bought were obvious duds, not accepting a charge the second time I charged them. The company I bought them from sent me a replacement, but this adds to my feeling that these are not very good batteries, regardless of the hype and promotion.

The DigiPower did rather well, considering that no rating was given on the packaging so I expected them to be cheap low-quality cells.

Lamp Test

Note that the Kodak curve doesn't correspond to the results of the flash test. It could not keep a moderate load as long, but it performed far better at a very heavy load. Perhaps the Kodak charger doesn't top off the cells as well as the MAHA charger, but the curve shape doesn't look like the left part may be missing. I interpret this to mean that the Kodak stand up better than the others under high drain.

Temperature

I've noticed that batteries fresh from the charger or when removed from a device are hot, sometimes too hot to touch. However, I'm also told that this should not be so, and that anything over 130 degrees F is wrong.

Well, it may be wrong, but that's the way it is. Using a bead-style thermocouple surface probe, I found that the highly regarded MAHA C204F smart charger ("the mother of all chargers") will heat batteries to over 150 degrees by the end of the charging cycle. The temperature quickly reaches around 120 degrees and steadily continues to rise. The peak reached with the MAHAcells was 156, and with the Kodak cells was 151.

I'm told by a representative of Thomas Distributing that it's not supposed to do this, and his doesn't get too hot to touch. Subsequent tests show that mine runs at 120-130 degrees (correct) until the very end of the charge cycle, when it shoots up to 150 or more. The problem may simply go unnoticed because of the short time it runs hot. Or, my unit may be defective. I plan to exchange it and test again with another one.

Meanwhile, the battery compartment of the Vivitar flash is measured to be 139 degrees F after 120 flashes, and a roasting 168 degrees after the Kodak cells were spent! This is hot enough to make the plastic start to smell funny. Clearly, the battery compartments of these devices were never designed with cooling in mind.

So, it would be a good idea to change the batteries in the flash after a period of heavy use, even though they are far from dead. The near worst case of firing full-power nearly as fast as it can charge will reach the problem point at around 100 flashes. So, change the batteries for a cool set after 100 flashes. If your camera needs batteries changed about every 100 pictures, change the flash too.

This is also another reason to look into external battery packs. The ones I've seen don't appear to be very much more powerful than a modern set of AA's, so I never bothered with them. However, it seems that a set of NiMH D cells can be turned into a pack with a holder and a wire with the correct plug on the end. This would give 8000 mAh, 5 times the capacity of AA's. More importantly, the current drain would be 1/5 as much relative to the capacity, as well. If this alone doesn't prevent heating (it may not matter, if heat produced is related to power consumed, irrespective of how much "stuff" in the cell is operating in parallel), the pack could be designed to afford better cooling, through the use of a heat sink and better air flow.

As for the charger habitually cooking the cells, this just doesn't seem right. MAHA's dumb charger heats batteries to 102 to 111 degrees (different cells in the same set reach different temperatures). I've not yet measured the temperature of the Kodak medium-speed charger that came with the camera, and I've heard (but not tried) that the TurboCharger 4000 only reaches 125 degrees. I've also heard good things about the Lighting 2000, and have ordered one. Stay tuned for more information.

Solar Power

I was annoyed to find all my flashes had dead batteries, and the spares were no good either. It seems that NiMH cells decay rather rapidly, and leaving them in a warm car makes their shelf life rather low. So, I won't keep my lighting bag in the car anymore, at least in the summer. I'll keep charged-up cells in the freezer until I pack them to go out.

However, it would be nice to have a spare set of batteries in the car, for times when I just take a camera with me, as opposed to planning a fancy shoot and packing a bunch of stuff. I've seen solar-powered chargers, and this seems a good solution. I can keep a spare set of batteries in a solar box, and they will stay charged.


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