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Method for Determining Battery Type and Remaining Battery Life

IP.com Disclosure Number: IPCOM000118644D
Original Publication Date: 1997-Apr-01
Included in the Prior Art Database: 2005-Apr-01
Document File: 4 page(s) / 117K

Publishing Venue

IBM

Related People

Petty, J: AUTHOR

Abstract

With a wireless adapter having a battery pack, the customer is provided with a "Percent of battery life Remaining" number as part of a status display. This number is organized by measuring the battery pack's DC voltage and then converting that reading into the "% life remaining" number.

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Method for Determining Battery Type and Remaining Battery Life

      With a wireless adapter having a battery pack, the customer is
provided with a "Percent of battery life Remaining" number as part of
a status display.  This number is organized by measuring the battery
pack's DC voltage and then converting that reading into the "% life
remaining" number.

      The battery voltage can be measured one of two ways -- when the
radio is drawing a lot of current because the transmitter is active
and when the radio is drawing virtually no current.  These two states
are referred to as "loaded" and "unloaded".

      Thereby, the battery pack accepts four AA batteries.  Some
customers use alkaline batteries.  Others use Ni-Cd batteries.
Unfortunately, these two types of batteries have very different
characteristics as shown below:
  Reading      Reading type     % life remaining
                                Alkaline   Ni-Cd
  5.2 volts      unloaded         56%       92%
  4.6 volts      loaded           73%       34%

      A first method of creating the "% life remaining" number was
optimized for Ni-Cd batteries.  However, when using alkaline
batteries, the readings stayed near 100% until the batteries were
almost exhausted.  Such behavior gives no warning about changing the
batteries.  If voltage readings were taken with the batteries
unloaded, as shown in the example above, the adapter would report 92%
of life remaining when in fact the alkalines were roughly 50% used
up.

      A way to determine what type of batteries are installed in the
unit is needed to accurately convert the battery voltage into a
figure giving the percent of life remaining.

      To make the status information accurate, the percent of life
remaining must be computed differently for the different battery
types.  This means knowing the battery type in use.

      A method of determining the battery type was recited that did
not require customer intervention.

      The method described is to detect the battery type by measuring
the difference between the battery voltage under load and the battery
voltage with no load.  This is a very good method to use with a
cellular phone since it is normal for the transmitter to turn on and
off which dramatically changes the load on the battery.  This method
could be applied to an automatic battery charger (which also needs to
know the type of battery installed).

      The difference in loaded and unloaded voltage for alkaline
batteries is much greater than the difference for Ni-Cd batteries.
For alkalines, the difference is roughly .7 volts and for Ni-Cd
batteries, it is around .37 volts.  Also, typically the unloaded
voltage of alkaline  batteries is higher than the unloaded voltage of
Ni-Cd batteries although  this is true only when the alkaline
batteries are relatively new (less  than 50% exhaus...