Page 96 - Lindens Handbook of Batteries

FACTORS AFFECTING BATTERY PERFORMANCE 3.15

4.5
4

3.5

3
0.1 second
pulse
Power, W 2.5 2 1 second
pulse

1.5

1
0.5

0
0 0.2 0.4 0.6 0.8 1 1.2 1.4
Load voltage, V
FIGURE 3.16 Power vs. load voltage at the end of a constant voltage pulses (undischarged zinc/alkaline/manganese
dioxide AA-size battery. (From Ref 2.)

on the battery chemistry, design, state of discharge, and other factors related to the battery’s internal
resistance at the time of the pulse and during the pulse.
The performance of a battery under pulse conditions can be characterized by plotting the output
power of the pulse against the load voltage, measuring the power delivered to the load by the short-
2
term pulse over the range of open circuit to short circuit. Peak power is delivered to the load when
the resistance of the external circuit is equal to the internal resistance of the battery. Figure 3.16 is a
power versus load voltage plot of the pulse characteristics of an undischarged zinc/alkaline/manga-
nese dioxide battery (AA-size) at the end of constant voltage pulses of 0.1 and 1 s. The lower values
of power for the longer pulse are indicative of the drop in voltage as the pulse length increases.

3.2.9 Voltage Regulation
The voltage regulation required by the equipment is most important in influencing the capacity or
service life obtainable from a battery. As is apparent from the various discharge curves, design of
the equipment to operate to the lowest possible end voltage and widest voltage range results in the
highest capacity and longest service life. Similarly, the upper voltage limit of the equipment should
be established to take full advantage of the battery characteristics.
Figure 3.17 compares two typical battery discharge curves: curve 1 depicts a battery having a flat
discharge curve; curve 2 depicts a battery having a sloping discharge curve. In applications where the
equipment cannot tolerate the wide voltage spread and is restricted, for example, to the −15% level,
the battery with the flat discharge profile gives the longer service. On the other hand, if the batteries
can be discharged to lower cutoff voltages, the service life of the battery with the sloping discharge
is extended and could exceed that of the battery with the flat discharge profile.
Discharging multicell series-connected batteries to too low an end voltage, however, may result in
safety problems. It is possible in this situation for the poorest cell to be driven into voltage reversal.
With some batteries, such as the lithium-sulfur dioxide primary battery, this could result in venting
or rupture.