Page 321 - Lindens Handbook of Batteries

BUTTOn CELL BATTErIES: SILVEr OxIDE–ZInC AnD ZInC-AIr SYSTEmS 13.27

1.3

1.2
Average discharge voltage, V 1.1

1.0

PR70/10 PR41/312 PR48/13 PR44/675

0.9
0 5 10 15 20 25 30
Discharge current, mA
FiGURE 13.26 Average voltage-current profiles for various zinc/air button batteries at 20°C.

The average voltage-current profiles for various sized zinc/air button batteries are shown in
Fig. 13.26. The average voltage of the battery falls as the current increases, until the battery becomes
oxygen starved. Once the battery is oxygen starved, it can’t support the load. Increasing the diameter
of the battery will increase its constant current capability.

13.9.7 Pulse load Performance

Zinc/air batteries can handle pulse currents much higher than the limiting current (I ) of the bat-
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tery. How high a pulse current level the battery can handle depends on the nature of the pulse. This
capability results from the reservoir of oxygen that builds up within the cell when the current load
is below the cell’s limiting current.
As long as the average current (I ) of the pulse load does not exceed the cell limiting current
ave
(I ), the zinc/air battery is able to sustain the pulse load. Figure 13.27 illustrates the resulting voltage
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profile of a series of Pr41(312) batteries with a I of 12 mA that had been subjected to an ever-
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increasing series of 1 s, 15 mA pulses over a 5 mA background current drain. In this illustration, the
duty cycle of the 15 mA pulse was increased from 10 to 50%. As the duty cycle increases, the aver-
age current is increased, reducing the overall running voltage of the cell. Since the average current
of the pulse regime never exceeded the battery’s limiting current, the battery was able to sustain the
pulse regime. If the pulse regime’s average current exceeds the battery’s limiting current, the battery
will become oxygen starved, and the cell’s voltage level will collapse.
Although the battery may not be oxygen starved, the voltage level achieved during the pulse
regime must be considered. In our example, if the device using the batteries doesn’t work below
1.1 V, increasing the pulse duty cycle will cause premature failure in the device. If, however, the
device works down to 0.9 V, increasing the duty cycle will have no effect on the function of the device.
Very high, short-duration pulses can be achieved by the zinc/air cell as long as the average current of
the pulse and the background current don’t exceed the battery’s limiting current and the voltage level
of the pulse doesn’t go lower than the functional voltage level of the device.