# What's up with "2/3 AA" batteries?



## Nubo (May 30, 2006)

I was looking for a way to bump up voltage in a small light, and ran across what are billed as "2/3 AA" batteries. I assumed 3 of these would be a plug & play replacement for 2 "normal" AA batteries. "Never assume"...

I opened the package and thought to myself, "these look awfully small....". Put a stack of 3 next to 2 regular AA, and the 3-stack is about 15 mm shorter! :huh2: 

Lol, what is up with these designations? Are these the same people who decided a 2x4 should really be 1 1/2 by 3 1/2 inches?

This seems strange. You'd think they'd try to squeeze in as much capacity as possible (i.e. take up the full 2/3 space), given that the energy density is already compromised. These little runts are maybe 3/5 AA, if that.

Ah well, they'll still work for my application. Just curious how these standards are set up. Does this same situation exist with the 2/3 A vs. "regular A" cells?


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## vortechs (May 31, 2006)

See this thread for my experience with 2/3AA NiMH cells, including some suggestions on how to charge them and how to make an adjustable spacer (using parts from Lowes) for using three of them in 2AA size applications: 
http://candlepowerforums.com/vb/showthread.php?t=115447


I also discovered that three 2/3AA cells are somewhat shorter than two AA cells. Oh well, at least it is easy to make the spacer.


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## Flash_Gordon (May 31, 2006)

As you have found out, the fractional sizes are are somewhat relative but not literal.

Here is a pretty good reference for future use: Battery Sizes 

Mark


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## vortechs (May 31, 2006)

There is also a list of common (and uncommon) battery sizes in the CPF Wicki: http://www.wiki.tjtech.org/index.php/Battery_Sizes


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## Nubo (May 31, 2006)

Thanks for the references.

I guess I should have looked for 1/2 AA instead. Those are listed as 30mm long, vs. 2/3 AA = 28.7mm long. :thinking:


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## Sub_Umbra (May 31, 2006)

Wow, this is pretty cool. It's like *"Secret Lives of the Sub Sized Cells".* Thanks for the links. Waiting for the six part mini series.


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