Crude DIY AA-Cell to D-Cell Conversion

“This article was first published at reThinkSurvival.com.”

I’ve been wanting to do this project for some time now. Considering that I have a few different D-cell devices (namely Maglite flashlights) and I have quite a few AA-cell rechargeable batteries, it only made sense to figure out convert AA-cell batteries to a D-cell so that I could ideally recharge my AA batteries and then use them to power D-cell equipment.

Now, I know they make AA-cell to D-cell adapters such as these:

But they only allow for conversion of a single AA-cell battery to replace one D-cell battery. Why is this a problem, you ask? The problem is that the capacity of a AA-cell alkaline battery is roughly 1/6 or less than that of a D-cell battery with capacities of between 1800-2600 mAh, while a AA-cell rechargeable battery is even worse (at usually around 1500 mAh). When compared to a single D-cell battery with capacities of between 12000-18000 mAh it’s obvious why Steven Harris (power guru of Solar1234.com and frequent guest on TheSurvivalPodcast.com) does NOT recommend using these adapters because you’re essentially working with an almost dead D-cell battery in doing so!

I looked a bit harder and found adapters that allow for conversion of two AA-cell batteries to a D-cell size:

That’s better but not quite what I wanted. Not to be deterred, I searched long and hard for an adapter that would allow me to combine even more AA-cell batteries with little luck. Actually, I did find some forum threads that indicated there are adapters that can convert three AA batteries to a single D-cell and eventually found a guy that makes and sells them on his own. The only problem was that they’re quite expensive. Anyway, I figured I would try my own hand.

Let’s start with looking at the sheer size difference of a single AA-cell as compared to a D-cell (click to enlarge):

Not only is there an obvious diameter discrepancy but a height shortage as well. Originally, I envisioned using a set of screws, washers, and nuts to combine the AA batteries together and be able to deal with the height problem too. The more I thought about it, though, I quickly realized that if I had followed through with what I wanted to do–using all metal to connect everything together–then I would have been directly connecting the positive and negative terminals, which is BAD… yikes!

I revised my idea and figured I needed something non-conductive to separate the positive side from the negative side yet still hold everything together. My first inclination was to use a wooden dowel but I didn’t have anything like that laying around, so I improvised and used a portion of a thick plastic coat hanger. In fact, here’s what I came up with (I was so proud) and I was going to show you how I put it all together but not so fast (click to enlarge):

You can’t see the insides, but there is part of a thick plastic coat hanger that has been drilled out with five AA-cell batteries around it, taped together, and a set of washers and screws on the top and bottom to not only hold everything together but to act as conductors as well; the only difference between the top and bottom is that the top included an additional metal nut to span the height difference between the shorter AA batteries and D-cell battery.

Like I said, everything was solid and very roughly the same shape and size as a D-cell. I even checked the voltage with my multimeter and it read correctly (at about 1.5 volts) so I was ready to test it… and here’s where everything failed.

I got out one of my trusty Maglite flashlight only to find out my contraption was just a bit too wide to fit! No big deal, I thought. I got out another flashlight (and another) and tried again. Still no luck. Apparently, Maglite is serious about their design tolerances!

I then decided that maybe five batteries was too much and removed one but even four batteries didn’t quite fit. Not to be deterred, I even tried a smaller plastic coat hanger figuring that the thicker one was just a bit too much. Even that didn’t work. Just to be sure I wasn’t crazy, I decided to test inserting four AA batteries, taped together and with nothing in the middle, to see if even they would fit. Guess what? That didn’t work either! So, no matter what I would have tried this idea wouldn’t have worked with four or more batteries… too bad I wasted a good hour before realizing that tidbit of information.

I decided I was going to try one last thing: to use three batteries instead. And, yes, they did fit in my flashlight just fine. Instead of going through the work of placing something in-between the batteries like before I was going to wing it and just see what happens. Here’s what I put together:

It’s basically three AA batteries taped together as before and with the same screw, washer, and nut configurations as before but instead of being solidly anchored to something in the middle (such as the plastic coat hangers) they are very loosely held into place by the tension between the screws in the middle of the three batteries. In fact, this really isn’t something that would stay together on it’s own very well. But, it works perfectly inside a Maglite flashlight because everything is smashed together by the force of the screw cap and attached spring.

I should say that I considered using slightly thicker screws than what I did in order to bite into the batteries better, but I didn’t want to risk a rupture and wind up with battery acid leaking all over my flashlights or me. I should also caution you that you certainly want to ensure the “streams don’t cross” if you will. In other words, make sure the positive and negative terminals never connect, which is quite possible if you use metal screws that are too long or do something else that I hadn’t considered.

In conclusion, I can say that this DID work but it’s not a very solid design and maybe not the safest either. Of course, by being able to harness the power of three AA batteries instead of one, I would be able to run my D-cell equipment significantly longer than I otherwise would be able to if I had to rely on AA batteries in an typical adapter for some reason. In reality, however, I wouldn’t consider this more than a last-ditch effort. In fact, I think I would just buy the 2x AA adapters referenced above and be done with it. All in all, it was a positive experiment especially since nothing melted, caught on fire, or blew up.

• Solar Equipment and Solar Battery Charging