back to article Pair of double-As give you cheap, quick charge

It's nighttime in Barcelona, you can't find your hotel and your phone battery is dead. Double-A batteries won't go in a phone so you're screwed, unless you've read the following advice. If a phone sports a removable battery then you can carry a charged spare, and there are numerous pocket chargers on the market, but they all …


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  1. Anonymous Coward
    Anonymous Coward

    I'll just pop

    into Maplins, oh I forgot, I'm in Barcelona its 2am and I can't use Google maps on my phone to find the local branch.... The batteries are flat.

    I'm a cynic aren't I .

    1. Anonymous Coward
      Anonymous Coward

      Re: I'll just pop

      not sure about cynical, think there's another word for what you have

      the idea is that, following the advice in the article, you keep the emergency charger with you so that you are prepared in advance and so don't have to go to the 24 hour Maplins that Barcelona doubtless has.

      Hope that helps

      1. Aqua Marina Silver badge


        Maplins is a fictional holiday camp loosely based on "Butlins" in the fictional seaside town of Crimpton-on-Sea, where Joe Maplin and his Yellowcoats have replaced the real-life Billy Butlin and his Redcoats.

        Maplin is an electrical store with over 15000 audio, video and computer products, components and accessories.

        1. Anonymous Coward
          Anonymous Coward

          Re: Hi-de-hi

          Ah the only one to see it!

          Clever you hi-de-ho!

        2. This post has been deleted by its author

      2. I. Aproveofitspendingonspecificprojects

        Re: I'll just pop into my hotel and get the emergency...

        Err... ummm...

        Can I borrow yer phone senor, por favor?


        1. Grease Monkey

          Re: I'll just pop into my hotel and get the emergency...

          @enigmatix but it's still stupid isn't it? An emergency charger and some alkaline batteries in your pocket at all times just in case? If you were thinking that far ahead you would just make sure your phone was always charged. Or maybe that you bought a phone with interchangeable batteries (what a radical idea) and carried a spare.

  2. gaz 7

    Progress :-(

    On most phones a couple of years ago, including mine, you can just swap the battery out, but user removable batteries are no longer fashionable - another "innovation" and "advance" brought to the market first by Apple.

    Mind you I still have a Psion 5MX which ran for weeks on a pair of double AAs anyhow - would love a modern version with bluetooth/wifi

    1. Adam Foxton

      Re: Progress :-(

      Isn't it just Apple that don't have user-removeable batteries? Every phone I've ever owned (just bought a Samsung Galaxy Note) has certainly had them!

      1. Peter H. Coffin

        Re: Progress :-(

        They're *technically* user-removable. But with the amount of levering of delicate hidden clips and the lack of obvious catches that modern phones are equipped with, I doubt that the covers would survive even a hundred battery swaps without breaking somehow. It's nothing at all like how phones were built even ten years ago, when batteries were obvious, massive enough to last for weeks, and intended to be swapped in a second or two by any untrained orangutan.

      2. J. Cook Silver badge

        Re: Progress :-(

        Motorola RAZR's battery is non-removable; same with the RAZR Maxx, IIRC.

        Usually a mobile's review lists if the battery is removable or not.

      3. Chloe Cresswell

        Re: Progress :-(

        My nokia E7 is also a sealed battery, it's not just apple..

    2. Anonymous Coward
      Anonymous Coward

      Re: Progress :-(

      The fact it didn't have bluetooth, WiFi and more importantly, a permanently on mobile connection is the reason the Psions lasted forever. They had piddly little CPUs and monochrome screens too. Their suspend mode will purely hold memory contents, everything else will be powered down unlike a phone which still has an active mobile connection and is constantly waking up to do stuff.

      A modern Psion would be as rubbish on power as a modern phone. It would still be cool to see one though.

    3. Jason Togneri

      Re: Progress :-(

      Yes, it's only Apple products as far as I can tell, every smartphone around here (Samsung, Nokia, Ericsson et al) have removeable ones. I do keep the awesome EBB-U10 around for my Galaxy S Plus, though, because it's an external battery as well as a hard shell, and as a bonus charges via USB port so there's no swapping of batteries (and thus no shutdown/reboot when battery is low) to worry about.

      As for the Psion, yes, I had a 3, 3C, Revo and 5MX and they were wonderful little things. However, throw on bluetooth and wifi and I very much doubt you'd get much life out of your 2xAA any longer...

      1. Andrew Moore Silver badge

        Re: Progress :-(

        The Bluetooth Revo ran for a decent amount of time on a full charge. However, the colour 5MX ran for just under an hour on a pair of AAs (both prototype units though).

  3. Anonymous Coward
    Anonymous Coward

    what I do...

    I've got a duracell four AA charger which has a removable plug section so it can fit nicely in luggage. It has a usb port to allow charging of usb devices from the charged AA cells.

    As it happens a standard 9v battery isn't the best option for charging as it's only 500mAh. A fairly standard AA is 2000mAh, maplin also make a 4x AA enclosure which connects to one of those 9v battery type connectors. The drawback with rechargeable AA cells is that you only get 4.8v but the chances are that this may well be enough without voltage conversion.

    1. This post has been deleted by its author

      1. The First Dave

        Re: what I do...

        A simple regulator like the one used in the article will NOT upscale your voltage like you suggest - they purely clip the voltage down, so need to make sure that the discharged voltage of your battery is sufficient.

    2. Grease Monkey

      Re: what I do...

      "As it happens a standard 9v battery isn't the best option for charging as it's only 500mAh. A fairly standard AA is 2000mAh"

      But remember those little things called Volts? The mAh capacity of a battery does not tell you how much energy it stores, you need to know that and the voltage. A 9V 500mAh battery stores about 50% more energy than a 1.5v mAh battery.

      Basically when it boils down to it for the same technology the amount of energy stored by two different batteries is comparable by their volume.

    3. Joel 1

      Re: what I do...

      Only problem with that Duracell device, is that they don't have the voltage on the data pins, and so won't charge an iPhone (in spite of being advertised initially to do that). As mentioned elsewhere, iPhones query the charging device to work out if they can pull high loads through it.

  4. Haku

    "Getting female USB sockets is hard"

    Not really, you probably have one kicking around already, some keyboards come with USB-to-PS/2 adaptors, and you can always buy the cheapest Chinese USB hubs you can find for the individual sockets or rewire it with whatever power source you wish to use so you can charge things from all ports of the hub (though you may need a 2A 5V power supply to cope with four things charging at the same time).

    However going down the DIY route of making your own USB charger it should be noted that some phones requrire a small amount of voltage on the data pins before they'll charge, notably Apple's products because some can take up to 2A from the USB port on wall adaptors for example but limits itself to only 500mA from a normal computer USB port. This can be set with the right combination of resistors.

    1. dr2chase

      Re: "Getting female USB sockets is hard"

      And that right combination of resistors puts 2 volts on D+ and D- for a 500mA charge. E.g., 75k and 50k between 5V and GND. See for more details.

      Some older Motorola cell phones expect to see something special on the "X" pin:

      This is rather annoying, since the USB cables I've dissected don't show any wires from their X pin; I have to buy a plug and hack it myself.

      I followed the ladyada instructions in a buck converter for bicycle use, and it worked fine; 500mA by 5V is 2.5 watts, with an efficient converter a hub dynamo can keep up, and various iDevices declared that they were in fact charging when I hand-spun the wheel. But it turns out that there is an affordable pre-built alternative (no idea if it works, just found it googling):

      1. Haku

        Re: "Getting female USB sockets is hard"

        When I built my custom light setup for my ebike (just a small setup, only 360 LEDs) I put a USB socket in the control box which is mounted to the handlebars, very handy for charging mp3/phone on the move.

  5. Anonymous Coward
    Anonymous Coward

    "On most phones a couple of years ago, including mine, you can just swap the battery out, but user removable batteries are no longer fashionable - another "innovation" and "advance" brought to the market first by Apple."

    Except the reality is very few people would carry a spare battery and making it removable probably adds cost, bulk etc.

    If you want to carry a spare there are LOADS of USB chargers available (as shown in this article) - many of which are barely bigger than a removable battery would be anyway. Plus they have the benefit of being able to charge other devices.

    Loads of devices have non-removeable batteries - for instance every Bluetooth headset I ever owned - it's not just Apple.

    1. Richard 15

      Making it removable would not significantly add to cost, but it would cut into the insane amounts of profit they make by having you take it into the store for replacement. Look into the after market alternatives vs doing it through Apple. But ignoring a full replacement, having the ability to swap in a spare is kind of important at times too.

    2. 100113.1537

      I get two ....

      batteries with every phone I buy. They come standard at no extra charge when you buy from Chinese suppliers.

      Used to be I had to out up with chinese instructions/software, but now they have the last but one version of Android so they are basically the same as anything else out there, just a lot cheaper. Slap in a pay as you SIM from whichever country you happen to be in and you're good to go.

  6. Anonymous Coward
    Anonymous Coward

    "As it happens a standard 9v battery isn't the best option for charging as it's only 500mAh. A fairly standard AA is 2000mAh, maplin also make a 4x AA enclosure which connects to one of those 9v battery type connectors. The drawback with rechargeable AA cells is that you only get 4.8v but the chances are that this may well be enough without voltage conversion."

    You said a (primary - non-rechargeable) 9v battery is 500mAh at 9v - a rechargeable AA might be 2000mAh but that is also at around 1.2-1.4v.

    The problem with not using a voltage regulator is your 4 x alkaline (Duracell type) cells are typically more like 1.6v out of the packet - so you would be feeding about 6.4v into your phone. The other problem is the voltage will sage under load and if it drops much under 5v the phone may decide to stop charging.

    Fully charged rechargeable AA cells are about 1.4v - so 4 of those would not even reach 5v and certainly not 'under load'.

    So the best options are either a genuine USB charger or you could go with the voltage regulator option but easiest to start with a higher voltage and drop down to 5v - would think at least 6v+ - so a 9v battery is fairly sensible / available option.

    1. Haku

      I have often used a set of 4x rechargeable AA's to charge my ageing trusty iRiver mp3 player and the various mobile phones I've had over the years. Works very well and have not had any problems with that method.

    2. Anonymous Coward
      Anonymous Coward

      re rechargeable voltage

      Modern aa rechargeables are 1.2v out of the charger, I'm currently running an arduino from four of them with no voltage regulation. Were they 1.6 it would blow up the microcontroller.

      Oh, I also metered them beforehand, just to check. They were 1.2 on the nose.

    3. Andus McCoatover

      'Black-box' thinking from most commentards.

      Where do you think your 5V or whatever is going? Into the 'phone's switch-mode PSU!

      It ain't that fussy, particularly as the charger's probbly made at Foxconn, and 5v is just a rule of thumb...

      (Why 5V? Thought mine was 8,4? Check when I get home...)

      IIRC, 5V was chosen in the dark ages (TTL chips being dark on the outside) as the transition between the Zener effect and the Impatt effect. Thermal stability.

      Definitely open to corrections - I remember this from a 1977 lecture.

      1. M Gale


        Yup. I remember finding this out myself. Basically TTL chips like to run between 4.8 and 5.2v. I remember the tutor saying how wonderful CMOS technology was because you can run some of the chips on damn near anything from less than 3v up to 18v or so.

        That said, I wouldn't want to take the chance on the phone's built-in power management being so smart. Regulator ICs are cheap and pretty efficient, and the phones are probably built in the same place as the chargers, after all!

    4. Stuart Halliday
      Thumb Up

      Not terribly accurate

      Typical Ni-MH is ~1.2V so 4x give 4.8V which is just within the USB 5V spec to work and unlike alkalines they keep their rated voltage steady until exhausted.

      If you have to use Alkaline (bad choice use Lithium instead) then place a 1N400X diode in series and that'll drop the voltage by 0.6V to give you around 5.8V at first but very quickly drops down to 5V and falling rapidly, alkalines don't keep a steady voltage.

      I see Maplin sells the Rolson Emergency Phone Charger too BTW.

      But this device doesn't like giving out more than 200mA before it packs in due to current drain abuse. I known, I've taken them apart to get the specs of the DC-DC converter.

      A 9V pp3 battery is not efficient. Apart from only rated at 200mAH, there will be a 4V drop across the regulator. This is power completely wasted. The Regulator needs at least 2V across it to work. So it wastes a lot of the battery.

      Much much better to use 4xAAA, 4xAA or 4xC or 4xD rechargeables Ni-MH batteries in a 4 cell holder from Maplin and a pp3 clip soldered onto an appropriate USB socket..

      If you want to be clever, add a 150ohm resistor across the +D,-D pins too.

      A decent set of AAA will give you 1000mAH, AA will give you around 2500mAH, C will give you 4000mAH, D will give you 10,000mAH.

      ASDA sells a tiny black 4xAAA holder with various USB sockets. You just need to short the diode it has if you use rechargeables.

      Better still buy a pack of Maplin's Hybrid AAA and you'll have 5V at 1000mAH on tap at any time as these Ni-MH cells only discharge very slowly so you can keep them in a drawer for 6 months without losing power like normal Ni-MH!

      I've been down this route with my HTC Desire HD phone. :)

  7. Tom 35 Silver badge

    simple voltage regulator

    If you can find such a thing for sale, I'm sure you could find a charger for sale.

    This would only be useful if you were stuck at home in a power failure and happened to have the parts in your parts bin to slap something together. I'm sure I do have the parts here, but expect even with the tech readers on this site there are very few people reading this that would.

    1. Comments are attributed to your handle
      Thumb Up

      Re: simple voltage regulator

      "If you can find such a thing for sale, I'm sure you could find a charger for sale."

      $0.54 (34.13p) on (part #512-LM7805CT)

      $1.25 on SparkFun (

      And, for the U.S.:

      Probably very expensive at RadioShack

      But like you said, most people will not have these in their house right this very moment.

  8. Will Godfrey Silver badge


    Use a switch mode in-line DC-DC converter. They are cheap (around a fiver) and work most efficiently when the input is about twice the output voltage (up to 95%). Readily available from all the usual sources.

    1. Vic

      Re: Pah!

      > Use a switch mode in-line DC-DC converter


      Using a linear regulator is ineficient (=wasted power). With a switchmode you can choose between step-up or step-down, so you can pick your battery type.


      1. Haku

        Re: Pah!

        I highly recommend the switch mode DC-DC converters from, yes they're a little expensive but very easy to use as you don't need any external components like smoothing capacitors etc.

  9. Steve Evans

    9v into 5v reg? Not exactly efficient... Burning off 4 volts to start with, and a PP3 is both pricey and low capacity to start with.

    Better to get 4xAAs and then use the 5v reg, you'll probably get a full charge from that.

    Better still...

    Work out where you are staying before you leave home and preload your google map tiles onto your phone before you start roaming ya muppet!

    1. Andus McCoatover

      How's about...

      4xaa's and a series diode? 'bout close enough.

      Alternatively, try the 'McCoatover' solution. Spare, fully-charged ancient old phone in suitcase, swap SIM if in shi*t. Worked for me a few times.

    2. El Presidente

      Better still...

      Work out where you are staying before you leave home and print out a pocket sized street map onto some old tech stuff called paper. In case your battery goes proper flat, like. It's what people used to do in teh dark ages.....

      Seeing at it's Barcelona I think Bill Ray ought to have taken the full experience option and asked a cab driver to take him to his hotel.

      Whereupon he would have been charged €20 to be driven round the City GTA style for five minutes before being dropped at the bottom of Las Ramblas.

      1. Steve Evans

        Re: Better still...

        Ah yes, you've not lived until you have had the Spanish taxi experience.

        It's still etch in my mind, strange considering my eyes were closed most of the time!

    3. Comments are attributed to your handle

      Not exactly

      Would have to be 5 AAs. Most simple voltage regulators (like this one) require the input voltage to be at least 1.5 or 2 volts higher than the output voltage.

  10. Captain DaFt

    I have a Sakar Jeep handcrank flashlight/phone charger that includes a cable with connectors for most cellphones.

    Came in handy last year when both the power and phone went dead at the same time. (Mr. Murphy loves to mess with me!)

    The big downside: about 5 mins worth of cranking for enough charge to make a quick call.

  11. Dave 126 Silver badge
    Thumb Up

    I lost my camera charger...

    so I invested in a universal lithium-ion battery charger. There are equivalents made by other companies.

    You twiddle the knobs until the two pins line up with the +/- contacts on your battery, and it detects the polarity and voltage automatically. It also has a female USB socket for charging things you still have the cables for.

    It's dead handy.

    Hopefully most phones will be able to charge over micro-USB soon... Apple and Nokia I'm looking at you! (You woulda thought that Nokia would see the wisdom is having their phones be easy to charge... after all, the ubiquity of Nokia chargers a few years back was a good reason for choosing their brand of phone!)

    I've tried the

  12. vagabondo

    £2.00 solution.

    I happened to wander into a "everything at a pond" shops yesterday -- Ineeded a cheap pen.

    For one GBP you can buy a device that holds 4 AAA batteries and comes with a selection of leads that enables it to be connected to most mobile phones. For another pound they had a pack of 11 zinc chloride batteries. These items are also available in the local "corner shop" for £1.99 each.

    1. Stu_The_Jock

      Re: £2.00 solution.

      A pack of 11 (ELEVEN) batteries ?

      That's a new one on me. Seen 10 and 12 before, but never 11.

      1. vagabondo

        Re: Re: £2.00 solution.

        Poundland, Argyle Street, Glasgow. Packs of AAA batteries:

        Kodak -- 11, Agfa -- 15, JCB -- 14, Kodak -- 6, Duracell -- 2, Sony --8.

      2. jonathanb Silver badge

        Re: £2.00 solution.

        It is Poundland. Pack sizes are made to a £1 budget and tend to be different to what is on sale elsewhere. They also tend to get smaller over time. Eventually they will go the same way as Woolworths did when they were unable to sell anything sensible for 6d.

    2. Graham Bartlett

      Re: "everything at a pond"

      But I suspect at those prices, it'll croak sooner.

      1. TeeCee Gold badge

        Re: "everything at a pond"

        Are you koi-ly suggesting that cheap batteries might be carp?


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