Squeezing the juice out of some AA batteries

[Ray’s] breadboard power supply lets you drain the last traces of power from ‘dead’ AA batteries. Electronics that are powered off of disposable alkaline batteries have a cutoff voltage that usually leaves a fair amount of potential within. Since many municipal recycling programs don’t take the disposables (you’re just supposed to throw them in the trash!) we love the idea of squeezing them for prototyping use.

His design uses just one IC, the MCP1640, along with a handful of passive components. The chip is a boost converter with a startup voltage of just 0.65V, which means the batteries themselves – normally starting life above 1.5V – can be used until they drop to about 0.3V each.

Above you can see the kit he is selling. But it’s an open source project and the circuit is so simple we’re sure you can build your own. Add that boost converter chip to your next parts order for around $0.40.

[Ray] made a nice demo video for the device which you can see embedded after the break.

74 thoughts on “Squeezing the juice out of some AA batteries

  1. My kids’ Leapster toys go through batteries like nobody’s business. All the “dead” batteries from those toys go into a pile for later use in flashlights and other devices that aren’t voltage-sensitive.

  2. As soon I start to see a device is a battery killer… I hack it and convert it to use a switching power supply. SMPS converters are about as expensive as a set or two of batteries so it’s a no-brainer when you don’t mind being tethered.

    I was just looking at this chip a month ago when I saw a new product post from Microchip… I thought of a couple similar applications, but not this one ;-) Good job, best of luck selling the kits!

  3. I haven’t read the article or watched the video yet. I’m at work and for some reason they block access to a lot of random sites. But, the info above made me wonder.

    Would there be a way to pull that charge out, possibly from a handful of ‘dead’ batteries, and use them to charge rechargeable’s? Like, use 10 ‘dead’ AAs to charge a set two rechargeable AAs?

    1. @T80: that’s an interesting idea and I thought about it. But I think the general advice is to not serial connect batteries that are at different conditions and/or voltage levels, because this will cause them to effectively charge each other and reduces usable energy. I need to look for more details.

      Of course the AASaver can be used to charge rechargeables too, since it bumps the voltage to 5V. By adding a USB connector, it can function similarly to adafruit’s mintyboost (which uses the LT1302 chip that can output higher current but also has a higher startup voltage requirement).

      1. OK, what I meant by ‘charging each other’ was not clear. Let me clarify it: when connecting batteries in series, since they have different internal resistance, the current flowing through them will be wasted more on those that have higher internal resistance, such as the really old ones. In other words, a battery that has lower internal resistance would have longer if it was not connected in series with other batteries that have higher resistance. This is the reason why we shouldn’t mix new and old batteries. But I guess if they are old batteries anyways, it wouldn’t matter that much :)

      2. it wont “charge” the flat battery, it will however reverse the cell. effectively charging it in reverse (what was the -ve terminal becomes the +ve) in a very very small way, most of the energy will go into making gas and heat eventually rupturing the cell and spraying hot wet battery goo everywhere. This isn’t an old wives tale, it happened in my mouse. Don’t mix cells with different charge states, they can go boom, literally. My missus came running, it sounded like a firework had gone off.

      3. @Valen:

        Why do things like that only ever happen to techies? I always read horror stories like that and they’re always written by techies. I’ve never seen a “normal” person mention an exploding mice or similar.

      4. I’m very interested in this idea as well. Currently have the solar LiPo charging circuit and a MintyBoost from Adafruit connected together. The LiPo charging circuit PCB accepts three different inputs (DC/Mini USB/bare naked DC +/- input on the board itself).

        My idea is to add a Joule Thief-style device as the third input, but I’m not sure the PCB will handle the minimal amounts of juice being sucked from the nearly dead AA/AAAs.

        The battery I’m using with this setup is a 6600mAh li-ion.

        Anyone have any ideas on this?

        Solar LiPo PCB: http://www.adafruit.com/products/390

    2. It would be pointless, really, to recharge batteries off other batteries. Recharging them from the mains costs way less than a penny, it’s a tiny amount of power.

      I suppose it’s pointless in general, really, since the point of batteries is their portability. It depends how long your device is going to run with this converter and some “dead” batteries. If it extends their normal life significantly, it’s a win. But if you have to use a heap of old cells to keep an LED going, it’s not got much practical use.

      The one practical use for DC-DC converters like this, is in stuff that takes 9V cells. 2×1.5v cells contain the same amount of watt-hours, and are much cheaper.

      1. I agree with you regarding the efficiency and cost of charging via dead batteries VS mains power… but how does your opinion on this change (if at all) when we remove the ability to charge via mains?

        The main purpose of my little homebrew project is to be able to operate for as long as possible (on a minimal scale) “off the grid,” to include the ability to charge via nearly depleted batteries. The need comes out of military necessity. Many of our various gadgets (night vision, laser designators, flashlights, etc) either require a lot of juice from these batteries or, by habit, we change them after a set period of time regardless of the charge left (for operational integrity, so to speak).

        Additionally, if we leave any batteries behind that have a charge then someone else (i.e. enemy) can get a hold of them and use them for their own purposes.

  4. Can this be tweaked to charge or power a USB device, like a cell phone or a palm pilot? An MP2 player? I never got the knack of electronics, but I agree with the not dead batteries being used. I have a bunch of them.

    I have a doodad I bought on eBay for less than $2 that takes 4 AA batteries and will charge my Clie’ about 2.5 times over. Even after it will not charge the Clie’ anymore, the batteries still have a lot of life in them, but I don’t have a way to use it. (What wasteful tech!)

    I recently retired the Clie’ in favor of a used smart phone. (All I really wanted was a phone I could play games on when I was waiting for someone or something.) Well, Android really sucks down some power! I am good for about 1.25 hours of game use and it is warning me to charge it. A device like this that would take 2 or 4 used batteries to maintain 5.2 or 5.3 volts for charging a USB powered device would be amazing!

    1. @MikeLinPA: MP2, nice :)

      See my comment above regarding using it to charge USB devices. In short, it can if you add a USB connector to it. But some devices such as the new iPhone are pretty picky about the charging current, which the AASaver may not be able to satisfy. For that the mintyboost is a better product.

    1. You Sir, win the shameless plug of the day award!

      For the record, I like Ray’s better… it operates longer, uses up more of the battery’s potential, has a higher output current, has a selectable 3.3V/5V switch on board, has an on/off switch, uses more commonly available AA batteries, works as an LED flashlight, is roughly the same price as yours and his is open source. Yeah I’d say Ray’s is way better.

      Please reply with an honest comparison and maybe you’ll get some people to buy yours.

    2. Yours do look nice also, as do the specs, but as already noted… you’re marketing to an open source community, without actually being open source yourself.

      If you’re listening, you might as well jump in the pool. :-)

      1. Heh mines is open source. I just noticed there is no schematic on my site but if you look around you will see. The schematic is the same for the boost boards i sell just uses a AAA instead for input. You can easily make this use a AA.

        Also 2 AA batteries are powering the device. Why isnt using 1 AAA better? You get double the performance. Having that 5v and 3.3v switch is nice, im not going to lie about that.

        I never said his wasnt good, just said i think mines is better and the main reasons are

        1. Single Battery Operation
        2. Fits better on a breadboard.
        3. Takes up 1/3 of the space of his.

        Im not posting here to try and sell more. I dont care about selling… You can tell since i keep my stock LOW. I make myself these boards and since i use LAEN PCB service from DorkbotPDX i get 3 boards and usually have no use for them so i put them up for sale. :)

        Ill add a image of the actual schematic now. But people should be aware… if you visit my blog which is the main site AtomSoftTech.com you can simply ask or email me for anything and if i can help i usually do.

        Sorry about the confusion and dont think i was hating on this dude because i didnt mean it like that.

        Thanks for the comments :)

      2. Good answers @atomsoft.

        I didn’t think you were hating on the article subject’s design (not sure you were referring to me on that, but anyways). Your boards do look good, but it seemed like you were plugging a closed source design that’s all.

        Your site’s well done also. Looks like you put some effort into the cart and CMS. Bookmarked. :-)

        Before I concluded you were closed source I looked for a company description, “About Us”. As you noted, it’s easy to forget downloads to the design files or github links.

        1. Thanks and i was talking about both comments but yours mostly :) Ill assume your name is Scott. Scott if you ever need anything (this goes to everyone here as well) , if i can help, you can bet i will.

          If you have any suggestions for boards or something cool please just feel free to email me and ill consider doing a post on it.

          While im not rich, i get money once in a while and love testing new things.

          Thanks for understanding.

  5. about the dead in series thing,,, i got a gehtto blaster that takes 8 D batteries, only problem is the heatsink for the main audio power amp is very close to one of the D batteries inside the internal holder.

    when a battery is used below freezing the battery’s internal resistence goes up causing the battery to fail, once you rewarm it, it works again… for a while.

    only problem is the WARM battery is now _COMPLETELY_ empty and has the dead-in-series mentioned problem as the others all held(whats left of) their charge, but just werent able to output it.

    when it stopped working, 7 of the batteries had 1.0v and the dead one had MINUS 1.5 volt!!!
    testing showed no real MINUS power, only voltage. lol :P
    so i guess it could have popped if the music went low/distorted/ect and then was not switched off…

    substituting a fresh AA or a weak C or even another dead D made it work for hours more!

    so the idea of this converter is VERY useful to someone that doesnt already have one.

    aka (broken) garden lights work on 0.75v – 1.5v
    with LED output at around 3.5v
    a dead D battery is WAY more juicy then a dead AA!

    PS: i intend on adding a heat-shield to the inside, so they ALL stop working at the same time and then start working happily later on when they warmup. :)

    PPS: aside from garden lights, i also have a nice little regulated converter; 2-5vin 5.0-5.5vout

    but none that input 0.6v and output regulated 5v.

  6. dead non rechargeable a/aa/aaa are often a nice source for zinc plates and carbon-rods.
    zinc: useful as battery tabs. with copper for vinegar or lemon juice battery experiments.
    carbon: to measure soil humidity or for arcs.

  7. Great project! However my solution has been to simply use rechargeable standard size cells (AA, AAA, 9V, etc). I have not used an alkaline in years, and the initial cost of the batteries has been payed back MANY times by this point.

  8. Just get some of the Eneloop rechargeables; they have about a 1 year self discharge.

    Just because it has an open circuit potential does not mean it has useful charge. I have seen a 75 year old battery with a 1.2 V potential.

    1. +1 … I don’t know why people buy disposable batteries, unless the electronics are equally disposable (throwies). Eneloops save money. Not that I care about the planet any (that job and worry rests exclusively with folks who have children).

    2. I have tried rechargeable batteries several times before. A fully charged rechargeable AA cell only has 1.25v. That is already too low for electronics. They wouldn’t run my (first) digital camera, and they won’t work in a device that charges my Clie’. (I considered hot-wiring a 5th rechargeable into the circuit, but I didn’t want to fry my Clie’ trying to save 8 batteries a year.)

      If they could either make rechargeable batteries that output 1.5 – 1.6 volts, or make devices that run at 1.1 -1.2 volts, rechargeable batteries would be a better solution. Until then, not so much…

      1. Yeah the voltage difference -is- a pain with rechargables.

        What I do is assemble the batteries into external packs (ie, 10×1.25 for ~12v) and plug the pack in as if it were a plug. It’s still tethered to something, but still portable.

        I have a LT1302 minty circuit to give me 5V battery packs when I need it, but something more “universal” (efficient DC voltage selection switching) would be an -awesome- hack. Otherwise I guess I’d need to build a bigger pack then I need, then slap on a linear regulator.

        For flashes and stuff, I know there are 1.65v zinc-based rechargables. Being way over 1.5v, they will potentially harm some sensitive (unregulated) electronics.

  9. Is there a way to connect 9V’s to this? This is great for AA and AAA’s.. but I have a number of 9V’s too.. Can’t use rechargables for the 9V’s so I end up with a bunch that are too dead to use… This would be a great way to sqeeze more juice out of them…

    1. @iant,

      This is (almost) the same as J Thief, just much more stable and efficient.
      With J Thief you lose (rough estimate) half the power (energy from battery), here you lose 15% or less.
      Also, with J Thief you don’t get “stable” output voltage, here you do.

      1. @Miroslav

        thanks a lot for your clarification. So it compares with JT but is much more efficient: very good to know!

        However, the JT components seems more readily available than the IC used in this build, and moreover can be found in trash electronic. Anyone can build one without any PCB and IC, and in my opinion it is a huge plus for JT! As far as you know, is there a way to increase its efficiency?

  10. It is similar to a Joule Thief in that they are both switching power supplies. It is different from the Joule Thief in that it is built on a monolithic IC by microchip instead of discrete parts.

  11. Years ago, I built a germanium transistor oscillator that would run at less than 0.25 volts. This was used to develop 4 VDC which powered a CMOS inverter chip that produced a good solid square wave and that drove an inverter. Total output, up to 35 volts charging a capacitor which then is used as a switching regulator supply.

    It will take a “dead” battery and run it until it drops down to well under half a volt. Current at that stage is the real problem, not voltaqe.

    The original idea came from old stle 0.55 volt photovoltaic cells that put out a good solid 100 mA or so but were normally useless without stacking them up. This circuit makes them useful easily.

  12. Why the hell did he put the parts list on google docs? He has a site, he has the other files on his sites, but then you get the google docs nonsense.

    Seems like a nice thing though and for the rest pretty complete.

    1. Wait, what’s wrong with the google doc? It’s easy to update, and since I already use it for making spreadsheets and documents, the changes I make get synced instantly with what’s published on my site. I don’t need to create a separate table and worry about syncing. I like it.

      1. Ray, I haven’t looked at your Google Doc… but have lots of experience with Google Spreadsheets and multiple users editing them. It’s ok, if you don’t have MS Excel, but if you DO have MS Excel it’s MUCH less painful that Google’s product. A web interface such as Google’s is slow and touchy. The power of MS Excel is unmatched, especially when it’s pretty commonly installed on all work PCs for you for free. Home computers YMMV depending on your core values and bank accts.

        I have been using Dropbox for syncing/sharing and it’s perfect! Even if you delete, or your friends/co-workers delete, you can restore very easily. Not to mention it’s free, until you want to start syncing your entire MP3 collection.

      2. Brett, I use Excel occasionally, but I still prefer Google docs for several reasons. First, it’s in the cloud and I can access it anywhere that I have Internet connection, whether Dropbox is installed or not. Second, I can publish a Google spreadsheet on my website, and the changes I make to the spreadsheet get reflected instantly on my website. It’s true that Excel is much more powerful, but I find the features provided by Google spreadsheet sufficient for my simple need (i.e. keeping inventory, email list, do simple calculation). Another reason is that my home machine runs Linux :)

        I do use Dropbox all the time, and I love it.

    2. @Whatnot: the ‘log in’ part is probably because I didn’t set the share settings correctly. A google doc can be shared as ‘public’, so that 1) it is searchable in the public domain; 2) it is visible to anyone with no login requirement. In any case, once it’s published this way, it simply becomes a html webpage. Other than the formatting looks like a ‘google doc’, there is no difference compared to writing an html table myself.

    1. One of the main drivers for his use of 555 is the cost – but this one describet here (MCP1640) is $0.60 in single quantities (+2R +2C +L), does not make much sense loking much further :)

      1. @Miroslav

        Does the MCP1640 regulate current? Or just limit voltage?

        Ryad’s circuit limits just the current, so he’s able to a drastically low resistor to LED ratio than you might need otherwise.

        Or maybe I don’t understand things well enough. :-)

      2. Actually if you buy 25 or more, the unit price of MCP1640 is only about 0.45.

        @ScottInNH: MCP1640 doesn’t regulate current directly. For that you probably need a current source, which can be implemented using an op-amp or transistor and diode.

      3. @Ray,

        It get’s even cheaper in 1000s, that’s why I said “in single quantity” :)

        Most of us here are still just doing prototypes, and counting the units we smoke out trying, it’s still well under 25+ :)

      4. @Miroslav: Oops, sorry that I missed that part.

        To be honest I tend to buy components in bigger quantity than I need, thinking that I can get the cheaper unit price and surely I can use them somewhere in the future. That’s why I ended up with having lots of components laying around that I have no idea when I will ever use them again :)

      5. @ScottInNH
        J Thief does limit the current, but that ends up as a very random value – too many parameters contribute to the actual value, so you should not count on that to be predictable, or repeatable value.
        MCP1640’s primary goal is to provide the stable output in Volts (2V – 5.5V) but it’s not that difficult to use a bit different setup to actually get a constant current circuit (one resistor less!)
        There are similar circuits that are designed just for that (LED driver), and they are usually equally cheap or just a bit more expensive.
        This format here is not quite appropriate for explanations and lessons, but if there is enough interest, I’m willing to compile something that others here might want to review and add more stuff.
        You might want to give Google a try and look for “constant current generator” – I suggest you try http://en.wikipedia.org/wiki/Current_source and start with the one in Figure 4 (transistor, Zener, resistor), if you understand that one, understanding how to modify MCP1640 is just one step ahead :)

  13. Just a note to anyone living in California:

    It is now illegal to put batteries (yes, all batteries, whether recyclable or single-use) in the trash in California. They are considered hazardous waste just like any other electronics.

    See calrecycle.ca.gov for more info. You can use earth911.com to find places to drop off your old batteries.

  14. Im thinking of purchasing one of these for when I’m doing wireless dev (Hate having to find power points around the house trying to find max range).

    My question is: How much noise is generated off this? And is it enough to mess with my 433Mhz circuits or decrease range by adding to the signal-noise ratio?

  15. I am using the MCP1640 at work already. Not as efficient as the MAX172x, but easier to obtain.

    One fine application is getting 3V or 4.5V out of a single primary or NiMH-cell. The circuit easily fits into the space of one AA:

  16. Hey @Charles Shults I found a whole pile of old 2N and NTE series power germaniums here.

    Wonder if this would work using a power infrared LED or array of them as a smaller alternative to a solar cell?
    Also worth a try, use a wifi chip antenna to make a trickle charger for PP3s.

    1. I’d expect to get just this side of 0mA out of an LED, or even a lot of them. They’re not designed to produce power like a solar cell is, and the surface area is minuscule. Using an LED like that is really only useful for sensors, I think.

  17. Could these be made really small and really cheap and put INSIDE batteries by the manufacturers? So the battery voltage is exactly 1.5 V until it’s really truly dead?

    Or put into a wafer-thin device that fits between the spring and the battery?

    1. No to the question of putting these into batteries. Batteries are pretty crude and cheap to manufacture, and batteries are only expensive for consumers at retail shops which have markup.

      But you are onto something with the idea to put this into a battery spacer. Not a wafer shim like you suggest, but put it into a battery “sleeve” like the kind you use to put AA rechargables into a “D” battery device. (Keeping mind that while AA and D are both the same voltage, you’ll never get the max current out of a AA that you would from a D, so the applications of a voltage boosting spacer are limited).

      I have a clock that really doesn’t run for long on rechargables (like a week), despite the battery still having 70% power left. A 3.2 voltage booster would help.

Leave a Reply


WordPress.com Logo


Twitter picture


Facebook photo


Google+ photo


Connecting to %s