What's the deal with AA batteries?

Discussion in 'General Electronics Chat' started by Cretin, Jun 16, 2013.

  1. Cretin

    Thread Starter Member

    Dec 13, 2012
    Why is it that my AA battery (rated 1.5) reads 1.2 volts on my MM, but doesn't provide enough juice for my wireless mouse to run?

    I did some research of my own and read that many devices have "minimum" voltage ratings required to operate, so that explains it but why is that the case? I mean theoretically shouldn't my AA battery power my mouse until my voltage is ~0 in my battery? If that is the case then also wouldn't it just make sense that as the voltage dissipates in my battery that it would just deplete faster and faster until it runs dry? Why is it that it just won't power the device at all? Is this shoddy engineering, am i missing something, or is this just business as usual to compel customers to keep buying more AA batteries??
  2. Kermit2

    AAC Fanatic!

    Feb 5, 2010
    A rechargeable battery will provide 1.2 volts when loaded. Is your battery a rechargeable one?

    A normal 'dry cell' type battery will provide 1.5 volts @ rated load WHEN NEW. When it is not loaded and has been used for awhile it can still read as though it has plenty of voltage when viewed with a voltmeter. The voltmeter does not draw a significant amount of current so the battery can maintain a high voltage when the meter is used, but when a device that draws, say 100mA is attached a used battery will not be able to supply the current and the voltage will fall to near zero.
    Try connecting your voltmeter to the battery while it is in the device and powered on. If the current drain is pulling the voltage down you will see it that way.
  3. Markd77

    Senior Member

    Sep 7, 2009
    Try using a 100 ohm resistor across the cell and see how much the voltage is. Completely draining a cell to 0V makes it more likely to leak [citation needed] and well designed devices will stop at around 0.8V because there is very little energy left in the cell.
  4. KMoffett

    AAC Fanatic!

    Dec 19, 2007
    Electronic circuits require some minimum voltage to function. It varies with the particular components involved, but there will always be a minimum voltage. A 1.5v AA Battery is considered dead in most applications at ~ 1.2V. Some circuit designs contain a "boost" regulator that can run an AA battery down to ~.5V, and still get 1.5V to the circuit. If you measured the battery voltage with the battery out of the mouse, the voltage when in use in the mouse will be even lower. I'd say you are getting about normal life out of the battery in that application. That's about what get in my wireless mice.