Type of Discharge
A battery may be discharged under different modes depending on
the equipment load. The type of discharge mode selected will have
a significant impact on the service life delivered by a battery
in a specified application.
Three typical modes under which a battery may be discharged are:
- Constant Resistance (“R”):
In this mode, the resistance of the equipment load remains constant
throughout the discharge.
- Constant Current (“C”):
In this mode, the current drawn by the device remains constant
during the discharge.
- Constant Power (“P”):
In this mode, the current during the discharge increases as the
battery voltage decreases, thus discharging the battery at a constant
power level (Power = Current x Voltage).
The discharge profiles of a "AA" size Alkaline Manganese Dioxide
battery under the three different modes are plotted in the following
sections.
Electrical devices require a minimum input power to operate at
their specified performance level. At the end of the discharge when
the battery reaches its end-of-life, the power output is the same
for all of the discharge modes and is at the level required for
acceptable equipment performance. In the example shown previously,
the minimum power level is 100 milliwatts and the battery end-of-life
or cutoff voltage is 0.8 volts. During the discharge, the power
output equals or exceeds the power required by the equipment until
the battery reaches its end-of-life.
