If you ever find yourself in the dark with burned out AAA batteries in your headlamp you may have a temporary solution if you have a 9-volt battery on hand. Recently I heard that you if you take a 9-volt battery apart there will be six AAA like battery cells inside. There is some truth to this but it isn't the case with every 9-volt battery. By way of peeling back the outer metal shell of a 9-volt battery I found that only some actually have AAA-like cells inside and while they were like AAA batteries and did in fact work I had to do some work to get them to power the headlamp.

The first battery I peeded the outter coating on was a Wallgreens Alkaline 9-volt battery. As you can see from the photo what I found inside was a set of stacked cells. Obviously I won't be able to put these into my headlamp. I guess I could Jimmy rig some wires for it but the task at hand here is to see if there are actually AAA like cells and if they work.

Stacked cells inside a Walgreens 9-volt battery.

After seeing the inside of the Walgreen's battery I was skeptical. Still I went ahead and opened this Duracell battery. Inside I found what appeared to be six AAA sized cells.

Peeling back the outer metal shell with a multi-tool.

The inner cells of the Duracell 9-volt battery.

At first the cells did appear to be just like AAA batteries but further inspection shows that they are actually both shorter and thinner.

Inner cell from the Duracell 9-volt battery next to an actual AAA battery shows the cell to be smaller.

In the following photos you can see the cells inside a petzl headlamp and a two-way radio. In the first photo you can see the cells come short of touching the metal contacts in the headlamp. I suppose one could bend them outward but they're still a bit thin so they'll wobble around from side to side. You'll need to stuff something in there or tape them to keep them secure and do what you have to to make sure the cells are touching the metal contacts on both ends.

Cells inside the petzl headlamp come short on hitting the metal contacts on both ends

In the next two photos You see the cells inside one of my two-way radios. They came short of hitting the metal contacts but I was able to stretch the springs a bit to get them to touch. They still wobbled around a bit so they would need to be taped down here as well. Just for a comparison I added a photo of real AAA batteries so you can see the size difference.

Side by side comparison with cells from inside a 9-volt battery and actual AAA batteries.

This is certainly something someone could use in an emergency but I wouldn't take apart a 9-volt battery that was in good working order if it was for something else that was important. As you can see not every 9-volt battery actually has the AAA-like cells inside. It's a gamble and if you find they aren't there the 9-volt may be useless at that point. I guess this is really something you do in a pinch.