New Battery For An HP50G


According to the author, the HP 50G is an awesome calculator. But as awesome as it is, it is powered off of not-so-awesome AAA batteries. These little batteries don’t last long under the load of the calculators awesomeness, so a mod needed to be done. The battery chosen for installation was a replacement battery for a Sony PSP. He was able to find one, including the external charge regulator board for $10.  Dropping it into the case and wiring it to charge off of the existing mini USB port looks fairly simple, very few actual modifications are necessary to the body. Unfortunately, they did end up with an LED protruding from the bottom that makes it wobble a bit, but they’re guessing that they get about 2x the battery life now.

14 thoughts on “New Battery For An HP50G

  1. TI-89s use AAA batteries as well. To solve the costly battery replacement dilemma, I bought a 4-pack of rechargeable NiMH batteries for about $10. They last for about a semester (~4) of light to moderate usage. A much easier solution, but perhaps not a “cool.”

  2. my ti89 titanium blew through 4 aaa’s about once a quarter, and the college store only sold cheapass aaa’s in 3 packs (what?) for more than a 2 pack anywhere else.

    maybe a nicad battery pack sized for 4 aaa’s would be an easier solution.

  3. Pretty cool idea, but why does the LED make it wobble? One can buy LEDs in all kinds of packages, including rectangular with a flat top. Most of the rounded LEDs (traditional package) I have also have a lot of extra plastic and can probably be ground down some on a dremel and polished with an emery board (the type used for buffing fingernails).

  4. I received my ti89 for free.

    but I have to say, it’s all about familiarity. I personally have no knowledge of what these calculators can do, but I know full well how fast most TI’s are and exactly what they can do.

    although i do have to agree that ti does charge a very large premium, those monopolistic jerks.

  5. Sorry for the double post, but:

    does anyone know of a cheaper source for a usb charging circuit like that?

    I have 6 li-ion cells from a laptop battery that stopped working, and the charging circuit for that is long gone…

  6. @Lessa:
    Most of the time you can tell how much battery you have left based on the contrast setting you’re using. On TI calcs its a 1-9 type deal, if you’re nearing the end of the adjustment you know you need new batteries.

  7. @xrazorwirex – they sell 3-packs because God’s Own Calculator, the hp48, uses 3 aaa batteries. They last over a year because it has a custom cpu (with 80-bit registers!) instead of the ARM in the hp50g. But, it cost too much to develop their own silicon (and keep up with speed and things like usb), so hp switched over. (incidentally, they dissolved the original calc group that made the 48, and the 50 was done by an outside group)

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