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

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  2. Additionally there is an easy way to discern the positive versus negative ends of a battery.

    Are you ready for this?

    …are you?

    A diode. For the sake of simplicity a LED (and a 1K resistor…you know, so you don’t blow out the LED). Since current can only travel in one direction through a diode (through a process leading sciencers have determined to be magic) the light will only turn on when you have the battery connected correctly. (And it has a low enough power requirement that you can test individual batteries thus eliminating the exponential combination problem.

  3. HAHA. I love the test screen. e^x-x
    *siren goes off*

  4. Hey, thanks for this. A few people come into my store asking for AAAA batteries. Now I have an answer for them!

  5. I had great fun trying to rip apart a 9v Energiser ™ branded battery. But following some cut fingers, I managed to mangle the case open and get to the cells inside. Interestingly, its quite easy to tell the poles apart because the +ve end has a small bump.

  6. I still can’t get it to work… I tell you though, I nearly split my finger open on the battery case. Not for the clumsy I’d say. Interesting idea, thanks.

  7. Great stuff! It worked, eventually. Hey derek, you’re right not for the clumsy
    what exactly was the problem? maybe we can help?

  8. Randall, your dainty needlenose are fine for this. Pry a corner of the Duracell’s seam with a knife and then use the pliers like a sardine tin key. I just did it to retrieve the 9v button-snaps for a project. Like most things, it’s about finding the archimedes spot.

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  12. @Mrten, “This works only with the ‘alkaline’ kind of 9V batteries, others are, as commented above, stacked.”

    Really? My opened _alkaline_ ANSMANN 9V is stacked.

    Also, nobody knows AAAA. Even battery companies misspell it! Finding AAAA: both difficult and expensive. Wikipedia has some model numbers.

  13. I too discovered this a few years back when need AAAA’s for a laser pointer, saves a fortune when taken from 9V as opposed to a package of 4A. huge markup thanks for the reminder of this usefully Idea.

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  15. Just saw that this got referenced in this month’s IEEE Spectrum magazine! (IEEE = Institute for Electrical and Electronics Engineers, kind of a big deal)

    Between the increasing commonality of this sort of reference and the You Tube type altering of reality, XKCD certainly is becoming part of Mainstream Internet Geek Culture.

  16. I just found out that the hack doesn’t work on Radioshack 9V batteries… they don’t have individual cells inside, just a sealed transparent plastic case with 6 “layers” of some sort inside. Just wasted a perfectly good battery and still need a AAAA for my bluetooth headset. :-(

  17. your website sucks batterys shouldnt be invented everything should be charged like the nintendo ds

  18. I was just browsing on Google for things to do with a 9v battery. I also saw a video on how to hack a 12v battery(i thinks its AA). The 12v batterys have eight of the small, flat, super expensive battery cells in them

  19. A Waste of time. When the battery is dead, I use a pair of small side cutters to open the old battery case and use battery terminals to make connections on various battery operated items. It’s cheaper than buying them at Radio Shack.

  20. you forgot to account for amps. the AAAA batteries in a 9v have about half the charge of a AAA. BTW your price of .7 is way over what I found. but even it wasn’t the difference in amps means that AAA last 1.8 times longer than the AAAA bringing the price up to $.594 for the equivalent of one AAA.
    btw brands and types to use if you choose to.
    Duracell-some but not all
    lithium 9v batteries have 3 3.2 cells
    NiMH have 6 1.2v cells
    some brands of cheaper carbon zinc only have 5 1.5v cells.

  21. Thats so strange. My ti-83 is also covered in white out on the back and has 9V component AAA batteries in it.

  22. I too discovered this a few years back when need AAAA’s for a laser pointer, saves a fortune when taken from 9V as opposed to a package of 4A. huge markup thanks for the reminder of this usefully Idea.

  23. I made this discovery about 8 years ago, while throwing dead 9V batteries at a wall (dead-end job…). Of course, I didn’t know I’d found anything interesting, because I’d never heard of AAAA batteries–but this is awesome, as I now need to power my laser pointer. Thanks!

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  25. A simple way to tell what polarity a battery is, and if it has a charge is to wet your lips and touch each side of the battery to your lips. You may have to open your mouth. If it tingles you have power. which lip tingles more will be the negative side.

  26. Dude, just use rechargeable batteries, they are way more economical after several charge cycles.

    And if a calculator takes 4 AA batteries, you could just jury rig the battery bay to connect to a 6 volt lantern battery (though it is disposable). Or you could just buy a cheap, rechargeable 6 volt lead acid battery from a specialty battery store to jury the calculator battery bay to work with.

  27. Tried it with two different batteries hoping to use in my jabra blue tooth headset. Did not like it with either battery! Matter of fact the headset does not like most batteries to begin with. Stupid headset! Sorry but I can’t endorse from my couple of tries!

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