How are the cells of 8.4V "9V" rechargeable batteries oriented?

Factual Questions
1

Alkaline batteries output 1.5 volts, so six cells are needed to make 9 volts. It’s easy to see how six cells would fit in the rectangular shape of a 9V battery, as seen here

Ni-Cd/Ni-MH cells, on the other hand, put out approximately 1.2 volts. To get 8.4 volts out of those, you’d need seven cells, right? How could seven cells fit in the form factor of a 9V battery without empty space?

Or, is that how they do it? Add empty space? I could see a 2x4 arrangement working, with one of those spaces just empty instead of a cell.

2

Well, I suppose I could have said that alkaline cells output 1.5V. Guess I need to preview 30 times before posting, right? :wink:

3

A 9v (PP3) battery contains six AAAA 1.5v cells (AAAAis a real, but uncommon cell size), wired in series to give 9V.
I haven’t checked myself, but I suspect that half of them will be positive-terminal-up and half down, in a sort of checker pattern, to facilitate the series wiring.

4

And I completely misread your question; sorry.

5

Every “9v” rechargable I’ve seen is actually limited to 7.2v.

Is there someone putting out a 8.4v rechargable cell? I was just shopping for batteries last week, and I didn’t see one.

6

At least some rechargeable “9v” batteries claim to make 9.4v to 9.6v, presumeably using 8 cells x 1.2v.

7

Nevermind my last post. Looks like there are some 8.4 and 9.6 rectangular batteries out there. I just haven’t seen them in the local hardware stores (or the DigiKey catalog) yet.

Glad to see it, too–the 7.2v batteries were just about worthless.

8

All the 9v rechargeables I’ve seen have a curved base; whether this is just to set them apart from alkalines or whether it reflects some kind of internal layout (such as disc-shaped batteries staked edge-on), I couldn’t say.

9

I have opened quite a few 9v batteries and never seen that internal arrangement of 6 cylindrical cells side by side. Rather, I have always seen 6 flat, rectangular, cells stacked on top of each other. In which case you can make them thinner and stack more.

10

Well, I’ll be a dead battery.

I always assumed that a 9v unit was a stack of 6 rectangular-cross-section cells in series, head-to-tail, requiring minimal strapping.

Now I see that they are 6 cylindrical cells instead. Why would manufacturers do this? A rectangular arrangement would provide a greater capacity for the same voltage.

11

Here’s a site showing a commercial rechargable “9v” battery. The label says “7.2v”, and the site says “Inside this plastic case you will find 6 - 120 mah nicad cells,” and they are all cylindrical.

I haven’t been able to find a picture of a rectangular cell arrangement yet.

Could rechargables be built different from non-rechargables?

12

This is from a Jaycar Electronics google cache, Using and Discharging Ni-Cad Batteries, so it doesn’t display well. I had to edit this extraction to make it readable. It doesn’t say anything about the internal cell shape. Italics all mine:

13

Why hasn’t anyone made a 9V cell? Seems like it’d be cheaper and more reliable.

14

What would you make it from? The voltage of a cell is a function of the materials used. You can change the amount of current a single cell delivers by making it larger, but you can’t up the voltage without switching materials.

15

The voltage produced by a cell is strictly a function of the chemical reactions going on inside the cell. Most cell chemistries are below 4v, and the most familiar and commonly-used ones are all around 1.5v. Designing a 9v cell would require that you find a chemical reaction that produced 9v, and found a way to package the reagents into a workable and economically-viable battery. I don’t know if that’s possible or not, but it’s not a simple matter of using stronger chemicals or making larger cells.

16

Well, as is becoming clear from the posts here (and as I’ve heard from other sources as well) that some 9v batteries are made this way, others are not. There are (at least) 9v batteries with 6 cylindrical AAAA cells inside, with 6 flat cells inside, and even with 3 3v lithium cells inside.

Maybe a company that makes both AAAA and 9v batteries uses the AAAA inside the 9v for economy, while a company that doesn’t make AAAA at all uses the flat cells.

17

AFAIK, a conventional wet or dry cell, regardless of the chemical composition(s) used, generates a maximum voltage in the 1 - 1.6 volt range. Maybe a chemist or a quantum physics major can explain why better than I can, but that’s the way it is.

18

That is, in fact, what it is in the majority of cases. I have opened batteries over the years (to keep the connector) and they were all like that. It is simpler and provides better use of space. I believe using cylindrical cells is exceptional and the battery will have less capacity.