Page 323 - Lindens Handbook of Batteries

BUTTOn CELL BATTErIES: SILVEr OxIDE–ZInC AnD ZInC-AIr SYSTEmS 13.29

1.4

1.3

1.2 3 mA
Voltage, V

1.1
5 mA

1.0
8 mA

0.9
–20 –10 0 10 20 30 40 50
Degrees Celsius
FiGURE 13.28 Discharge voltage level of a Pr44 (675) zinc/air battery as a function of discharge current
and temperature

of oxygen diffusion is limited by the actual oxygen used in discharge, but the situation changes when
the demand is oxygen limited. At increased elevation, the barometric pressure goes down, as does the
partial pressure of each gas present, including oxygen. As a result, the limiting current of a cell decreas-
es as it operates at higher altitudes where the concentration of oxygen is lower than it is at sea level.
The effect has been noted by active hearing aid users who have hiked to greater elevations. Airliners
are pressurized to a “pressure altitude” around 8,000 ft. This is enough to decrease limiting current by
about 25%. The relative partial pressure of oxygen at various points on interest, expressed as a percent
of the oxygen available at sea level (760 mm barometric pressure) is displayed in Table 13.7.
Tests of cells in a chamber that had been evacuated to simulate the pressure at altitude declined
in limiting current (i.e., the current that can be made to flow if the CCV is held to 0.9 V) and in

taBle 13.7 Partial Pressure of Oxygen at Altitude
Barometric Partial pressure Percent of
pressure of oxygen sea level
Elevation (ft) (mm Hg) (mm Hg) pressure Points on earth
–1500 802 168.0 105.5 Dead Sea, Israel-Jordan (–1317 ft)
–500 774 162.5 101.8 Death Valley, CA (–282 ft)
0 (sea level) 760 160.0 100.0 London, England
500 746 156.7 98.2 montmartre, Paris, France (423 ft)
1,000 733 153.9 96.4 Vaalserberg, netherlands (1,053 ft)
2,000 707 148.4 93.0 High Willhays, Cumbria, UK (2,037 ft)
5,000 633 132.8 83.2 Denver, CO (5,280 ft)
10,000 523 109.8 77.2 Cascade mountain, Canadian rockies (9,836 ft)
20,000 349 73.4 46.0 mt. mcKinley (20,320 ft)
30,000 226 47.48 29.8 mt. Everest (29,028 ft)