Testing the 9V Battery Hack (or: Assault on Battery)

Kipkay over at Metacafe has posted videos showing how you can take apart a 9V battery and use the cells as AAAA or AAA batteries (he has a similar trick for 12V -> 1.5V button batteries. I have played with batteries a lot in my life and never knew this. There was some speculation on reddit that it was a hoax of some kind, so as a good sciencer (like a scientist, but we don’t get the lab coats) who really didn’t want to get started on the morning chores, I decided to try it myself with a new 9V I had sitting around. I learned a couple useful things.

Duracell batteries are harder to open than the video implies. My dainty needle-nose pliers weren’t enough — I had to go find larger clampy ones. The edges of the case are also sharp. This would be very tricky to do in a car somewhere without tools.

He tells us these are AAAA cells, which makes sense. You know, I didn’t even know AAAA cells existed until I encountered a tablet stylus that used them. The handy thing is that they can double for AAA batteries in most cases — they just won’t last as long.

I decided to test them in my TI-86. One important thing he doesn’t mention is that there’s no reliable way to tell the polarity once you’ve disconnected them, so mark them somehow as you take them apart. If you’re just guessing, you’ve got 16 combinations to work through.

I didn’t think about this, so I cut them apart and folded over the remaining half-tabs on each end, then tested them all with a multimeter to get the polarity (my digital multimeter is missing, so I couldn’t get exact volt-readings).

I put them in the calculator. It didn’t turn on. I added a bit of aluminum foil at the contacts to make sure they were all touching.

It works!

So, in conclusion: This is a decent way to get AAA batteries in a pinch for a bit less than what they cost in the store, although I don’t use 9Vs for much, so situations where this is helpful are gonna be a bit rare. AAAs in a pack of 8 usually go for about $0.70 a battery, 9Vs for around $2 — so $0.33 per AAA. AAAA batteries are rare enough, and marked up enough, that if you have something that uses them this could be a worthwhile main source.

185 replies on “Testing the 9V Battery Hack (or: Assault on Battery)”

  1. Jeremy: HP finally made the true successor to the 32SII, and not that abomination called the 33s? Sweeet!

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  2. The lozenge vs AAAAs is pretty much a matter of spec vs. implementation. The spec requires it to be of particular dimensions and voltage but the implementation is up to the manufacturer.

    Stacks are probably easier if you aren’t also making AAAAs. AAAAs are probably easier if you’re already making them (even if they aren’t finished quite the same).

    Stacks is what one will normally see on pictures in books on science aimed at young kids (when we learn that the 9v things are correctly “batteries” and the 1.5v things are correctly “cells” and we remember the distinction for about 5 minutes before we go back to calling both “batteries” like everyone else, unless our inner nerd insists upon a moment of pedantry), but maybe that’s just the matter of what was the norm at one time.

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  3. I wonder what it would look like if I opened a 9V I have lying around that I ran 12V of current from an AC adapter through overnight. The battery is bulging, nearly cylindrical.

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  4. Please, think about the nature! Buy rechargable batteries! (well, i’m french. Is it the right word? batteries you can uh… fill again with power? repowerable?)

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  5. Lars: The 6 cells are in series, so if you’re drawing 400mA from the battery, it’s equivalent to drawing 400mA from each cell. Therefore, each cell will also be rated at 400mAh, but at 1.5V. So, actually, you’re wrong.

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  6. See, you should have had me for a physics teacher in HS. I cut up a 9V years ago and I drag it out to show my classes every year. Same with a big ol’ cylindrical capacitor!

    I really enjoy your comic, by the way. Thank you.

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  7. Pingback: Free
  8. Sure, you can get batteries cheaper at the IKEA… But what’re you gonna to do when the raptors take over the local IKEA?

    Hunh?

    You know what you’re gonna do?

    Hide in a corner while we disassemble our nine volt batteries to power our calculators so we can plan a counter-attack!

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  9. What is that foil on the calculator? It wouldn’t happen to be the foil from gum wrappers, would it? I did that to my calculator a few years ago, and now I can’t for the life of me remember why I would do such a thing, or where I got the idea.

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  10. I think the part where one blog posts to another blog is called a “trackback” or “ping”, “pingback” or something like that. I see it a lot. I’m surprised that it hasn’t been used to death by spammers in an attempt to get more traffic or a better pagerank. Maybe it turns out that it doesn’t do anything for pagerank.

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  11. I forgot to mention that my dad had been given a few promotional penlights that used AAAA batteries. This trick may be a good way to get cheap A^4 batteries because they are so stinking hard to find and expensive.

    Yes, rechargeables should be favored, but I haven’t seen any rechargeable A^4 batteries, and the only rechargeable 9V batteries I’ve seen was over a decade ago and were only NiCd, not the newer NiMh or rechargeable alkalines. Which is better to use depends on the use. IR remote controls that last over a year on batteries are probably far better off with just plain alkalines. High-current devices should be rechargeable.

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  12. In regards to the white on the calculator, it does look like it submitted to white-out at some point, as did my own CASIO scientific at one point. The size of the screen and the overwhelming number of buttons was causing me to freak out at important moments, such as in the middle of physics exams. To solve this problem, I took the liberty of writing on the back, in large friendly letters, the words ‘Don’t Panic’. It thus scores slightly higher over my sister’s Texas instrument, which doesn’t have these words and if I remember correctly, was slightly more more expensive than mine 😀

    Apologies to Douglas Adams for the extensive ad-libbing.

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  13. And hey—I see that you too are a fan of the excellent TI-86, with its unobtrusive menus, efficient complex number notation, and complete lack of advanced graphing and CAS features! Hail and well met! ^_^

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  14. BTW, if you are looking where exactly, you will basically have to click 7 times on “next”

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  15. so I tried this because my brother’s ti-89 ran out of batteries. I was pulling the half tabs off because they had torn, and the battery casing literally shot out of my hand, nearly into my eye. the sound of it was so loud my ear hurts.

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  16. Vicki: I did exactly the same thing. (Seventh grade math class, though. At the time, I was utterly astounded by the number of buttons.)

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  17. It’s “may you live in interesting times” dude! an altogether different proposition.

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  18. So, I don’t know if you noticed, and I didn’t read through all 75 comments, but the batteries are actually easily visibly identifiable, the one side has a physical ring indentation, in my experience, that’s the positive side.

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  19. “These are AAAA not AAA, they are just close. You’re also trying to compare 400mAh at 9V and a AAA is 1000mAh at 1.5V. mAh are the rated milliamp hours that battery is rated for, not a statement of energy stored.

    You need to take (mAh * V) = Wh (multiply by 3600 for Joules)

    Watt hours are how you compare different batteries unless they’re at the same voltage.”

    But the whole point of this is to show you that 9v batteries are close enough to six AAA batteries that they can be substituted for them. So that means that the each 1.5v cell has (shock) ~400mAh – coompared to ~1000mAh for buying the AAA batteries in the first place. Also the AAA batteries actually fit in properly. This hack is only really useful if you can’t find any AAAA.

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  20. Well it looks like your battery hack screwed up your calculator’s floating point handlers. e^[pi] – [pi] should be 20.

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  21. @JeffDM:
    Actually, if you look at Harbor Freight Tools, they have a line of NiMH 9V, I think rated for 700mAH.

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  22. It seems like it would be more useful to do this in reverse. Take 6 AA batteries and turn them into a 9 volt battery that would last longer. Interesting experiment either way, though, thanks

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  23. Max Kuipers seems to be the only one to look at the screen of the calculator. I’m dissapointed with all of you. 83 posts and only one mention of the actual comic.

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  24. Battery hack update: bunches of AA size batteries inside a 6v lantern battery! However, they seem to be low-charge cells, and some 6v are made from larger 1.5v cells inside.

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  25. I have the same calculator! but mine is the silver edition! jealous much?

    I liked this little fact, but i’m wary of opening up batteries as ive seen the massive stain on my uncles desk where he tried to open up some kind of battery and it leaked battery acid everywhere. this is the same uncle who once took apart a nappy (diaper to you) to see how it worked…

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  26. seen the massive stain on my uncles desk where he tried to open up some kind of battery and it leaked battery acid everywhere. this is the same uncle who once took apart a nappy (diaper to you) to see how it worked…

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  27. I have a TI-86 and some 9-volts. This looks like a fun project just for the hell of it.

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  28. For real fun, find an old Polaroid SX-70 film pack battery. These were wrapped in lots of black darkroom paper, but they had warnings every few folds: DANGER DO NOT OPEN THIS BATTERY PACK, WARNING CORROSIVE SUBSTANCE INSIDE and so on. They must have had a dozen warnings, and a yard or two of wrapping. Needless to say, we kept going until we hit the metal plates and corrosive substance which wasn’t all that nasty. Maybe Polaroid was afraid someone was going to eat it.

    SX-70 batteries were hot stuff when they came out. The reusable flash was serious and the film shot out of that camera lickety split. I’m not sure what kind of battery it was, but it was more powerful than anything on the shelf at the drugstore.

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  29. Cool. But if I really needed power for my TI 86 and only had a 9V battery, the same thing could surely be accomplished without opening the battery, using a resistor in the loop?

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  30. Note: the silver on the calculator is foil plating from chewing-gum wrappers. If you’re careful, you can peel the foil up from the wax paper and use it to faux-silver-plate things pretty impressively. That’s what remains from a plating I did one day in high school, six or eight years ago, so it’s pretty durable.

    I did the exact same thing to my (now retired) Ti-83 in HS! I wonder how many other people have done that to their calculators…

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  31. “One important thing he doesn’t mention is that there’s no reliable way to tell the polarity once you’ve disconnected them, so mark them somehow as you take them apart. If you’re just guessing, you’ve got 16 combinations to work through.”

    That is a bit off don’t you think? Did you not notice that only one end of these batteries has a bevel where the other end does not? That would be a good start in distinguishing between each ends polarity after taking them apart. That is providing the specific battery you are working with has these same distinguishable features but it is likely they do.

    Also 16 combinations? Where did you pull that number from? There are 6 batteries each with 2 ends that would total 12 but that is even over kill since each of these batteries are the same you eliminate 5 leaving one battery with 2 ends. Only one of which is positive and one is negative so it should not be overly difficult to interpret which end is what now should it?

    Cool experiment though, to bad it has already been done yet you do have some good pics of it.

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  32. 4 batteries in the calculator, 2 ends : 2^4 = 16. Do you /really/ want to go math pedant here?

    Deep love for the TI-86. Got mine from a yard sale for $3 out of a $1 remote-control bin. He wanted to charge me three because it was ‘So fancy’, so I let him.

    Also a plug for TiCalc.org(above).

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