Computing stuff tied to the physical world

New AA battery option

In Hardware on Aug 19, 2010 at 00:01

Today might be a good day to set aside your dislike of Apple for a moment…

There is a new battery pack + charger option on the market:

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In Europe, this combination costs €29.95, and it gets you 6 rechargable batteries plus a charger.

The specs are what make this thing particularly interesting for low-power battery-powered devices:

  • each NiMH AA cell holds 1900 mAh charge (rumored to be rebranded Sanyo Eneloops)
  • the batteries are reported to retain at least 70% of their charge for 2 years
  • battery lifetime is reported as being at least 10 years (with recharges, of course)
  • the charger drops to 30 mW “vampire” power draw once the batteries are charged

To start with the latter: I’ve verified it. When charging, there’s a small yellow LED and it draws less than 4 watts. When done, the LED turns green, and power consumption drops to 0.18W. Then, after 6 hours, the LED goes off and the power consuption drops to… zero! At least on the very sensitive SBC-500 I used.

This is a very big deal!

It means you can permanently leave these chargers plugged in, with a few spare AA’s. No cost, no waste – simply a way to keep a couple of cells fully charged and ready to go.

It’s also perfect for JeeNodes, using the standard 3x AA battery holder:

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That’s 4.1V when fully charged. And JeeNodes will work with them all the way down to 3.3V, i.e. 1.1V per cell. Also, unlike LiPo batteries, running NiMH batteries down won’t do them any harm.

At last, I can stop wasting alkaline batteries… I’m probably going to replace all of them in the months ahead!

  1. At last a non overpriced product from Apple :-) (6 eneloop batteries cost about 20 euro’s, so that 10 euro’s for the charger)

    Any idea how long this keeps a node (with for example a rooms sketch) up and running?

  2. Hmmmm… Not bad. Although I can’t believe it’s taken you this long to dump Alkaline! I don’t think I’ve bought any of those for years!

    The charger I bought here in the UK was this one from Maplin

    Comes with 4 x 2500mAh AA NiMh batteries. Will charge from mains, USB or 12v car (all connectors included) and will charge 4 AA or AAA at time.

    £22.99 (€27.90) I have no idea who makes their Maplin branded batteries, but I haven’t had a problem with the sets I’ve had for a couple of years. I used them in my camera flashes. They currently have 8 packs of the same batteries for £9.99!

    So I can still continue my dislike for fruit themed things :-D

  3. IMHO for really low power usage scenarios I would suggest using one single AA sized Li-SOCl2 3.6V 2400mAh battery. It’s supposed to have a shelf life of 10 years. Assuming this means it retains 80% of its power after 10 years, this is a lot better.

    Ok, I cannot recharge them but who cares? In my sensors I have calculated a battery life of 9 years with these things.

    Yes, calculations and an assumption mixed with specs. Only practice will prove it wrong or right. Let me get back to you on that in 9 years;-)

    See also discussion in:


    ofcourse I couldn’t resist commenting on this post;-)

  4. @mdamen – Nope. Not as long as I want them to, a rework of that sketch is (fairly high up) on my todo list.

    @steve – Most NiMh/NiCd cells I’ve used didn’t keep their charge very long (weeks). The news is that these Eneloop units do

    @stef007 – If you get that sort of life out of a battery, then yes that sounds like an excellent choice. I’m secretly hoping to improve the room node to the point where I can get say 2 years of life out of one charge – keep in mind that the motion sensor eats a continuous 40..50 µA.

    Then, with these chargers, a run-down battery is no longer a problem, or even a hassle: just swap the two sets and move on.

    The battery you’re referring sounds a bit like this one. I’ve got a couple of those left, but I’m not going to sacrifice them before getting the room node current down to a really good level under all conditions.

  5. Yes that’s exactly the one I’m using (with the wires attached to the poles). They cost about 5.5 EUR @conrad. Have not yet found another source around here.

    Indeed, motion detection is a lot more difficult to get low power because its sensor must always be one and must be polled regularly to see motion. A lot different then my sleep-measure-transmit sensors.

    A trick I use sometimes to avoid the current drain of other plugs/chips when atmega is in powerdown, is to power these plugs or chips via a DIO on the atmega and switch it to 0 before sleep.

    This works pretty good for the outputplug and for the luxplug. But ofcourse you must not forget to wait for the plugs controllers to wake up. So in that case I do something like this:

    • sleeping for a long time, DIO’s powering plugs at 0, so they are completely dead
    • wake up, set DIO’s to 1 to power up the plugs
    • sleep again but leave the DIO’s to 1, give the plugs the time to “boot” while the atmega sleeps a while longer
    • wake up again and now do your stuff. Sometimes the plugs need to have time to perform their measurement (like with the sht11 and pressure plug), in that case sleep a while again and fetch the results on wake up.
    • now goto winter sleep again with DIO’s to 0

    I suppose switching the motion sensor module on and off when sleeping is not going to help you much? Ofcourse it depends on the “boot time” of the motion module/chip and the frequency at which your polling the sensor…

  6. @Stef This post really couldn’t have had your name on it more even if it had been titled “Attn: Stef”

    @JCW, Not keeping a charge for weeks? Really? I remember NiCds doing that, but I have/use loads of NiMh (excessive collection of camera flashes) and I’m forever just grabbing the next set from the bag. Occasionally I’ll throw an unused set into the charger just to make sure they are fully charged, and invariably within 2 minutes the charger is flashing its “done” light at me.

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