General Building an external battery pack...

Discussion in 'Android Devices' started by notaguru, Jun 12, 2010.

  1. notaguru

    notaguru Well-Known Member
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    Apr 22, 2010
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    I think the standard battery is 1100mAh (1.1 amps at 3.7V for one hour), which is generally good enough for me, but there have been a few times on travel when an extended battery would have been useful.

    USB provides 5 (FIVE) volts to the unit, which is regulated down to charge the internal 3.7V single lithium cell. It should be trivial to build a battery pack to recharge any product that is so powered. But you cannot use external lithium because that would also be 3.7V.

    I'm thinking of NiMH (nickel metal hydride), each cell of which provides 1.2VDC. Four cells in series would be 4.8V, and there are now 3000mAh (three amp!) AA cells out there, so NiMH AA cells should more than triple battery life for the Eris. Of course, you could use five such cells to get 6.0VDC, then regulate down to 5, but that would add complexity.

    I didn't find any posts on building such a thing, and wonder if anyone's done it.
     

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  2. copestag

    copestag Well-Known Member
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    or you could just go online and buy a small charger that runs off a single AA for $2-$3

    a single AA charger is usually good for 2-3 charges........ and you can use rechargeable AA in it......

    theyre just slightly larger than the AA battery itself and usually have a keyring on them so very convenient

    and btw the standard battery is 1300 mah
     
  3. notaguru

    notaguru Well-Known Member
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    I'd prefer to buy rather than build - thanks! Such a charger must have a boost circuit to get the 1.2V up to 5V, so that price is amazing.

    Where can I buy such a thing?
     
  4. copestag

    copestag Well-Known Member
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    Ebay is where I seen them that cheap......... but if you Google you can find them all over the place for about $10 or less

    I just googled "eris AA battery charger" and got plenty of cheap results
     
  5. gruss

    gruss Well-Known Member
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    For a couple more bucks I've seen Li-ion external packs too in the 5000 mah range. Nothing terribly outrageous. I've gotten pretty used to using my wall charger and just swapping batteries carrying a spare isn't a big deal, my wife has my 3500 mah battery now, I miss it.
     
  6. notaguru

    notaguru Well-Known Member
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    Those single-AA units work for me.
    Looking around, they all have a sort of buck-boost circuit to output the requisite 5VDC from a 1.2 or 1.5V AA cell. Output is apparently about 300mA, which is enough to operate the phone's circuitry when in use, and to charge the battery when it's not.

    A terrific solution, and thank you!

    --------------------------

    Found 2xAA chargers with built-in flashlight, from Asian sources. 350mA output, and $5 or so.
     
  7. psiclist

    psiclist Member
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    May 29, 2010
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    After reading this thread, I went online and found a plastic box for 4 AA batteries with a USB port for $9.95 with shipping. I already have the batteries, and I can use the original cord with it. Battery life problem solved.
     
  8. FortKnox

    FortKnox Well-Known Member
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    Care to share the make & model, as well as your satisfaction with it?
     

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