What's inside a 9V battery? More batteries! (…and why you never see a AAAA)

And this is the reason I read www.edn.com. Incrdible post.

Has any one ever opened a 9v lithium?

i took a 9v apart and one of the batteries exploded does that mean acid came out?

I have been taking apart this type of 9V batteris and use 4 of them to replaced the expended one inside the J-pack 6V battery (for economical reasons). It should be awared that this type of cells can swell up or even explode when not bounded by the metal housing. I have the experience of having a couple of the loose cell sitting in the component drawer and exploded by themselves for no apparent reason - not being connected and no shorting. The force broke the plastic drawers!

I also remember disassembling (probably in the 60s or 70s)and finding six rectangular cells. Thinking about this a bit, I would think the rectangular cells should be more space-efficient (and therefore have more capacity) than cylindrical AAAA cells of the same chemistry. But I guess they changed over because it let them stop manufacturing the rectangular cells which probably weren't used anywhere else.

There are still some 9 volt alkaline made of the stacked cell type. Gold peak makes them this way as does Rayovac for some but not all. Rayovac uses both types and actually the different designs have different discharge curves. For people who have a need to individual AAAA cells, mostly lazer pointers as far as I have seen, the AAAA in the 9 volts can be used in place of individual AAAA cells if you just put a sleeve on them after dissasembling them and they are much lower cost this way than purchased in 2 pack consumer version.

What is in the batteries?

I've seen AAAA's in retail packaging at Menard's; 2fer ~$3; one of the few places that I found them. I use them in a Streamlight LED penlight. They were one of the 1st to do so, & they come in different colors, incl. UV, & w/ a goose neck. They're about the dia. of a #2 pencil in a HD Al housing, kind of a micro-MagLight.

Indeed in the 80's these batteries were a pack of rectangular cells... I remember making radio jammers with them, taking out half of the cells. This gave a 4.5V battery and half the space of the 9V pack left free to fit a 7413 IC with its output shortcircuited to its inputs. The IC oscillated at around 30 Mhz, tunable by squeezing the battery package a little bit. The 3rd harmonic jammed the radio of our janitor at school that time, he never suspected the battery next to his radio did this...

If more designers of small devices knew what was really in a 9V, they'd use something else. There's really not much capacity available but these were handy when designing for a 5V project. But I was dismayed when I bought a noise cancelling aviation grade headset (I'm a private pilot) and found it was powered by a 9V! It ran through batteries like crazy. Regarding the quad-A, I think Energizer offers these for commercial sale.