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. Right, except that the typical 9V battery has a max of ~400 mah, while a typical AAA battery is up to 1000 mah. So, these will last less then half the amount of time as typical AAA batteries.


  2. I learned of this a few years ago when I replaced the main circuit board in an old Angel LCD paintball marker with one from a Generation-E Matrix. The old Angel board was powered by a NiMH battery which fit in one of the marker’s tubes, whereas the Matrix board was powered by a regular 9v battery. I learned that if I took the casing off the 9v I could unfold the cells and fit it all in the Angel’s tube.

    Also, I discovered something interesting. Different battery manufacturers connect the cells in different ways. As pictured, the cells in Duracell 9vs are connected by flat pieces of metal that are soldered to the cells. In Energizer 9vs the cells are separate, and press up against small boards with traces in the top and bottom of the battery. This was less convenient for my paintball purposes, but would probably be better if you wanted to use the individual cells as AAAA or AAA batteries.


  3. Very cool.
    Rumor has it you’re in the Cambridge area. If you ever wanna do team trivia with some people from fark.com, We go to John Harvard’s monday at 9pm.
    This isn’t commentspam, I swear. Us farkers love your comics.

    You should have my email from this comment.


  4. Note: The title of this page says “Blog Archive”. Seeing that this is actually a blag, you may want to fix that.


  5. I have that calculator. I thought those things went into the ether after I got past my first 3 semesters of college, because I never heard anything about them again.


    Nor did I have any need to use mine.

    Awesome info though!


  6. 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.


  7. Hack’s don’t catch on enough, most people are never willing to go far enough to bother. I’m more concerned stripped cells more likely to leak.


  8. “Right, except that the typical 9V battery has a max of ~400 mah, while a typical AAA battery is up to 1000 mah. So, these will last less then half the amount of time as typical AAA batteries.”

    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.


  9. I opened up lots of 9V batteries as a kid and found that they’re not all constructed this way – some contain a stack of 6 rectangular shaped cells, kind of like a pez dispenser.


  10. If the whole battery is 400mAh at 9V, and the cells are each 1.5v connected in series, then each cell is 400mAh at 1.5V.

    In terms of energy per dollar, it’s actually a loss at the prices you stated above for AAA batteries, as you’re paying more than 40% of the price for 40% of the total energy.

    With regard to opening 9V batteries:
    I’m not sure what brand does this, but I’ve seen a couple that don’t have individual cylindrical (AAAA) cells inside. These have a plastic casing inside the metal shell with the electrodes and electrolyte paste layered to make six cells in series. These batteries wouldn’t be very useful for salvaging AAAAs.


  11. Interesting stuff. I remember taking apart a 9V in the 1980s and finding it was a vertical stack of six lozenge-shaped cells, rather than six long cylinders side-by-side. This is (IMHO) a change for the better….


  12. I hate to tell you, but I think your calculator is having floating point issues calculating e^pi – pi. Everyone knows that should come out to 20.


  13. I took apart a 9V long ago and was surprised to see it was AAAA’s in there. It’s also kind of icky in there so…. just buy your AAA’s from the store. Or steal ’em from your relatives’ remote when you visit or something.

    I also have that calculator, but mine’s OVERCLOCKED. Um, yes it does graph a bit faster than yours does. It’s not worth it though, it takes some brutality to get it apart – it’s not really meant to come apart, and you’ll have little nicks on the edges afterward.


  14. You’re forgetting one minor detail in your cost calculations. The cost of a product includes the labor to produce it. Somehow I doubt people will start ripping apart 9V batteries just because it’s 40 cents cheaper than a fully packaged product. I also doubt that the performance characteristics and safety profile of your makeshift batteries are the same.

    I’m just sayin’. Carry on, Sciencer~


  15. From the pictures it looks like there are crimps in one end of each cell. Couldn’t you use that to tell the polarity?


  16. Now THAT I LIKE! – never took one of those apart. 6 x 1.5 = 9

    Way back when, there were huge batteries called A and B (often used to power ‘portable’ radios in the vacuum tube days) so they had high voltage output to power the tubes (and short life) They were also made by connecting large numbers of smaller cells together, and wrapping them in a (cuboidal cardboard) box, with a couple connectors on the outside. Dad had a Bendix (formerly i aviation electronics), and I have an old Zenith ‘transoceanic’ (which was a workhorse in the army in WWII) which used these batteries. Fortunately, both also could be plugg in (to the wall there are a couple sources for duplicating these old batteries by using scads of AAs.

    Never heard of AAAA. Now, as things so often go, I should run across something that uses them shortly.


  17. You suck. TI is for grade school. Real men use HP calculators with reverse Polish notation (which I guess is kinda like the Reverse Cowgirl for Engineering classes).

    My bro took apart a 9v battery when we were younger and it was made out of AAAA batteries just like that. So when it hit the intarblarg, I just shrugged my shoulders and wondered why it took people so long to figure this out.

    I also tend to think that devices don’t use 9v batteries anymore, with low-dropout voltage regulators and less-than-5v Vcc voltages and DC-DC converters and stuff, so I’m betting that optimizing the output of a 9v battery with lozenge cells or whatnot isn’t worth it anymore.


  18. I would have thought that a fairly reliably way of working out polarity would be to use a meter, after all doesn’t everyone have at least a basic multimeter in their toolbox? Or failing that, a marker pen during disassembly?


  19. John: Er, those are exactly the two things I mentioned. I used the meter to determine polarity because I forgot to mark them as I disassembled.

    JeffBell: I created those crimps when I cut the flat metal strips connecting them.


  20. It’s fairly easy to tell the polarity on cylindrical cells like these.

    The negative end (anode) is almost always part of the cylindrical case, and is generally flat with no large bumps. The negative end is pretty clear on the top center cell in the second picture.

    The positive end (cathode) is generally a cap or button connected a rod leading into the interior of the battery, and is isolated from the casing by a plastic insulator. The positive end looks like the top left or right cells in the second picture (the black plastic insulator is also visible around the button contact).

    You can also see a single crimp in the metal casing circling the cells on the positive end of the cells (the metal casing is connected to the negative contact, and the crimp is around the plastic insulator insulating the positive contact).


  21. Awesome, thanks for the info, I’ll be sure to remember this when I need some cheap AAA batteries.

    By the way, your comic rocks.
    Keep it up man.


  22. I thought about the crimps as a means of polarity indicator, as well. In any case, wouldn’t it be easiest to solder a small, flat metallic cylinder to the + pole? That way, you’d have almost retail AAAA batteries 😉

    About RPN, TI and HP: I have heard rumors of a mod that enables TI users to use that. Using google, I couldn’t find satisfactory results. Does anyone know more about this? Is it a hoax?


  23. This works only with the ‘alkaline’ kind of 9V batteries, others are, as commented above, stacked. Dunno how it is over on the other side of the pond, but over here in Holland IKEA sells those AA and AAA batteries for ridiculously cheap (as in E0.075-0.15/apiece). Seeing that you put AAA’s in devices that use no to almost no current (remotes, wall clocks, etc), it might be wise to get those el-cheapo ones instead of the expensive Duracells.


  24. For this cost calculation:

    If you really have to use batteries, like for calculators or sth., it would be the cheapest to use rechargeable batteries aka accumulators. I don’t know about the energy prices in the US (I guess they are low compared to Europe) but I’m pretty sure, it’s worth it.

    However, I know, it is kind of difficult to get them, I was searching quite a while for them in the US and Canada, but I know they are outthere… I wonder why it is sooo hard…

    Not to mention the eco aspect…


  25. ift, you’re wrong. Ampers and Ampers hour are dependant of voltage, so 400 mAh at 9V is not 400 mAh at 1.5v, that’s why Bill Batteryman tells you to convert the units to Watts/Hour (using Voltage) which is the correct way to compare the batteries.


  26. But can you do the opposite, and hack together a faux 9v battery using the AAA betteries that everyone has lying around all the tme anyway?


  27. @toshiro and A Half-Polish Programmer:
    There’s an application for the TI-83 to do basic calculations available at the following link. Personally, I’ve never been impressed with TI’s interfaces… And I think my HP48SX is kinder on the batteries, too! ;c) I think I understood RPN calculators by the age of 10, before I ever laid my hands on any calculator that assumed algebraic inputs.



  28. @ A Half-Polish Programmer:

    I love the HP 15C. Am glad to know that there are other reverse-polish devotees keeping it real out there.


  29. Lars:

    Actually, he is right. 400 mAh at 9V is not 400 mAh at 1.5V, but it *is* equivalent to 400 mAh at 1.5V *six times*, which is what you get out of one 400mAh 9V battery.


  30. And here I thought I was going to be clever and be the first to criticize for not using an HP. In case you RPN junkies weren’t aware, HP finally released the true successor to the 32SII a couple of months ago, the 35S. Check it out. Big ENTER keys are back in style, baby.


  31. Matthew: I think that you could do the reverse in theory, but the problem is that these are AAAA sized batteries so they wouldn’t fit in the place that holds the 9v battery unless there is a lot of wiggle-room for some reason. In a pinch though… I’d guess probably. You’d probably need a cheap battery casing or some soldering skills to get them to stay connected though.

    Also, I think a lot of people are missing the point of this hack. 99% of the time, there is not reason you will ever want to use this to get AAA batteries, but it is a tool to remember if you need to be “heroic”: “Stand Back I’m Going to Try Science”


  32. The Hell…

    “The Blog with No Title » Blog Archive » Lori’s back! Says:

    August 22nd, 2007 at 1:17 pm
    […] has a cool article up about how you can get some cheap AAAA or AAA batteries from a 9v in a pinch. Here it is if you are interested. And yes, I know it wasn’t his idea initially, but I think he runs […]”

    That’s my blog, but I have *no* idea why it posted it on here. Does WordPress do that automatically if you link to an article on another site? Odd. Spam unintentional I promise! 🙂


  33. Here’s my question: was the calculator betrayed at some point by some white out? Because the back of the ol’ 86 seems awfully not black, which isn’t normal.


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