# Why are batteries round in cross-section? **URL:** \ **Category:** Factual Questions\ **Created:** [May 3, 2002, 4:08pm UTC](https://boards.straightdope.com/t/why-are-batteries-round-in-cross-section/107088 "2002-05-03T16:08:43Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![SmackFu](https://avatars.discourse-cdn.com/v4/letter/s/53a042/32.png) [@SmackFu](https://boards.straightdope.com/u/SmackFu)\ **Post date:** [May 3, 2002, 4:08pm UTC](https://boards.straightdope.com/t/why-are-batteries-round-in-cross-section/107088/1 "2002-05-03T16:08:43Z")
It seems like for most products, there is extra space around the batteries that could be filled up by more “battery” if they were square instead of round. But they’re all round, except nine-volts, which are still rounded. Any ideas? ---
**Author:** ![ticker](https://avatars.discourse-cdn.com/v4/letter/t/d07c76/32.png) [@ticker](https://boards.straightdope.com/u/ticker)\ **Post date:** [May 3, 2002, 4:16pm UTC](https://boards.straightdope.com/t/why-are-batteries-round-in-cross-section/107088/2 "2002-05-03T16:16:26Z")
WAG originaly the most common application for these cells was flashlights, where a round cross-section made ergonomic sense. Since that time tradition dictates that newer sizes (AA, AAA etc) would also be round. ---
**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\ **Post date:** [May 3, 2002, 4:22pm UTC](https://boards.straightdope.com/t/why-are-batteries-round-in-cross-section/107088/3 "2002-05-03T16:22:00Z")
I just wanted to point out that if you [open up a 9-volt battery,](http://www.howstuffworks.com/battery4.htm) it’s composed of several round cells. There are rectangular cells. I hear they are less efficient for the given weight, though I’m not sure about the exact reason. Even laptop battery packs often use round cells - the Sony Vaio battery packs are cylindrical, and my ThinkPad battery looks like there are two rows of circular cells inside. ---
**Author:** ![ticker](https://avatars.discourse-cdn.com/v4/letter/t/d07c76/32.png) [@ticker](https://boards.straightdope.com/u/ticker)\ **Post date:** [May 3, 2002, 4:32pm UTC](https://boards.straightdope.com/t/why-are-batteries-round-in-cross-section/107088/4 "2002-05-03T16:32:45Z")
Could there be some edge-effect going on here? A round cell would have better surface to volume ratio than a square cell so that would make some sense. Perhaps some current leaks back along the surface creating a short circuit, reducing battery shelf life. ---
**Author:** ![toadspittle](https://avatars.discourse-cdn.com/v4/letter/t/c0e974/32.png) [@toadspittle](https://boards.straightdope.com/u/toadspittle)\ **Post date:** [May 3, 2002, 4:37pm UTC](https://boards.straightdope.com/t/why-are-batteries-round-in-cross-section/107088/5 "2002-05-03T16:37:25Z")
My guess is that you want the material to be equidistant from the anode/cathode. If the cell were square in x-section, the gunk in the corners probably wouldn’t get used up as well, and the energy potential might be wasted. this page has a cool cross-sectional diagram: > **[404 - Duracell Batteries | AA, AAA, Rechargeable, Coin Button](https://www.duracell.com/en-us/404-not-found/)** > > 404 - Duracell Batteries | AA, AAA, Rechargeable, Coin Button Oh, and I direct your attention to the awesome photo of a dismembered 9-volt battery at [howstuffworks.com](http://howstuffworks.com) (not square after all!): > **[How Batteries Work](https://electronics.howstuffworks.com/everyday-tech/battery4.htm)** > > Battery experiments can help you better understand how electrochemical reactions work. Find out how to conduct your own battery experiments. And we all know that those freaky 6-volt lantern batteries are likewise composed of smaller round cells, right? ---
**Author:** ![toadspittle](https://avatars.discourse-cdn.com/v4/letter/t/c0e974/32.png) [@toadspittle](https://boards.straightdope.com/u/toadspittle)\ **Post date:** [May 3, 2002, 4:38pm UTC](https://boards.straightdope.com/t/why-are-batteries-round-in-cross-section/107088/6 "2002-05-03T16:38:40Z")
holy simulpost. ---
**Author:** ![Why\_A\_Duck](https://avatars.discourse-cdn.com/v4/letter/w/13edae/32.png) [@Why\_A\_Duck](https://boards.straightdope.com/u/Why_A_Duck)\ **Post date:** [May 3, 2002, 4:44pm UTC](https://boards.straightdope.com/t/why-are-batteries-round-in-cross-section/107088/7 "2002-05-03T16:44:55Z")
If you want cool battery info, check [this](http://www.energizer.com/learning/howbatterieswork.asp) out.