Seems I killed some of my batteries. I bought some cool 8-cell holders with coax connectors, which allowed me to form them into battery packs that I could plug into the charger or plug into some device to power it. However, I forgot to build into my devices the ability to detect when the batteries were dead, and since they don't all go dead at the same time, some of them were drained to the point that a negative voltage was applied, which pretty much kills them.
I've taken steps to prevent this in the future by making a little device that plugs onto the coax connector and monitors the voltage, sounding an alarm when it becomes low. This seemed like the best solution since one application is to use the batteries to power cameras when I go on bicycle rides, and in that case I'd rather get a warning and change the battery manually than have it just cut out on me.
Anyway, this now put me at a shortage of batteries, and unfortunately Walmart wants $10 for 4, and eBay has spoiled me to the point that I can't pay prices like that anymore.
So I had a look at what eBay has to offer. There are some very cheap NiMH batteries, but as many reviews and some honest sellers state, their capacity is only 300 mAh despite 3000 mAh being printed on the label. Fucking scam manufacturers.
So I found some with the brand "Lumsing" that were supposed to have a capacity of 2850 mAh, a larger capacity than any previous battery I've purchased, but not an unreasonably high capacity either. They're available from many sellers, all of whom I assume are the same since they're all in Plainfield, Illinois.
I also needed some alkaline batteries for my steel drum toys. As it turns out, Walmart is crazy expensive on batteries too. Duracell and Energizer are about $1 per cell, and Rayovac isn't much cheaper. They do have some generics too, but they're not with the other brands, they're hidden away somewhere past the checkout aisles, which I didn't discover until a later visit.
Anyway, not finding the generic batteries prompted me to go to the "Everything's $1" store, where I found Sunbeam brand cells, 4 alkaline for $1, or 8 carbon zinc batteries. Curious how these compared to the more expensive Duracell batteries, I put them in my tester too.
Anyway, I'm tired of graphs, so let's just do this in text:
After the concept of "internal resistance" finally clicked for me, I added a "mAh" field to my software, so no more estimating mAh from the Joules.
Batteries 0 & 1 are old Energizer NiMH cells rated at 2300 mAh, which I tossed in just for comparison. I can't say how they compare to past tests since for some reason their missing the numbers I taped to them so I don't know which cells they are. ...and come to think of it, I forgot to number the new cells. Fuck.
Batteries 2 - 5 are the new Lumsing cells, rated at 2850 mAh.
Battery 6 is an alkaline Sunbeam cell.
Battery 7 is a carbon-zinc Sunbeam cell.
I have a separate script that tells me how much of the capacity was delivered while the output voltage was still above certain thresholds, namely 1.0 volts, 0.9 volts and 0.8 volts. Here's its output:
Overall, I'd have to say they're not quite 2850, and definitely unlike the Duracell & Energizer which always seem to test better than their rated capacity, but they're not far off, and for being half the cost of those brands and still having a better capacity, they definitely seem like a good deal. I just hope they don't have some other problem, like perhaps that capacity quickly disappears over time.
As for the alkaline battery, I see that the Duracell alkaline that I tested 2.5 years ago held out for almost 6 hours in the testing device, dumping 8.8 kJ by that point. The Sunbeam alkaline held out for a little over 6 hours, dumping the same 8.8 kJ by the time it dropped below 0.8 volts. I don't have a mAh number for that Duracell since I wasn't doing mAh at the time, but the voltage graph looks pretty similar too, so I'm going to guess the mAh would be the same too.
Now perhaps there's something to the Duracell batteries to justify their triple cost, like that ten year shelf life they make such a big deal over, but at least in terms of just tossing them in something and draining them right away, it seems that $0.25/cell batteries work just as well as $0.75/cell batteries. So I think from now on I'll just buy the generic alkaline cells.
The carbon zinc battery isn't so clear, but I'm leaning towards declaring it a waste of money. It does say right on the package "ideal for low-drain devices," and my battery tester isn't exactly low drain and so the fact that the batteries took a dive right at the start isn't much surprise. However, the interesting thing about the mAh rating is that it ignores the battery's internal resistance. Thus, even though I was draining the battery far too fast, and thus I won't receive the same Joules that I would if I drained it more slowly, the mAh I get out of it should be the same either way. The chemical process inside the battery has so many electrons to move, and it's going to be the same number regardless of whether I drain it slowly or quickly. So a slow drain should produce the same mAh, just at a higher voltage.
So when we look in the first table at the mAh rating of the carbon zinc cell, it's nearly half of the alkaline's mAh rating, which is in line with the carbon zinc's cost being half of the cost of the alkaline batteries. So they're perhaps as cost-effective as alkaline cells in low-drain devices if you don't care that you're replacing them twice as often, but why bother? Just get the alkaline batteries which are just as cheap when you consider that they'll last twice as long.
Still, I may have to perform a low-drain test to verify that, as I'm not certain about it, and there could be money to be saved if it turns out I'm wrong.