Specifications

MARATHONNORCO AEROSPACE, INC.
NICKEL-CADMIUM AIRCRAFT BATTERIES
24-34-00
Page 2
APR 15/06
Charge
Charging results in the conversion of electrical energy to stored chemical energy. The active materials, in a
discharged condition, are cadmium hydroxide in the negative plates and nickel hydroxide in the positive
plates. With the application of a charging current, these active materials undergo a chemical change. The
negative material (Cadmium Hydroxide) gradually gains electrons and is converted to metallic cadmium
(Cd); the positive material is gradually brought to a higher state of oxidation (loses electrons). As long as
the charging current continues to flow through the battery, these changes will take place until the active
materials in both electrodes are completely converted, at which point, overcharge commences.
Toward the end of the process (as the materials approach a full charge condition), and during overcharge,
gas will be evolved and released through the cell vent. This gas results from the electrolysis of the water
component of the electrolyte. The gas evolved at the negative plates is hydrogen and at the positive plates
is oxygen. The amount of gas evolved depends upon the charge rate during the period in which the cells
are being overcharged. After complete conversion of the active materials has occurred, the further
application of charge current will only cause further electrolysis of the water and I
2
R heating.
Discharge
Discharging results in the conversion of the chemical energy stored in the cell to electrical energy. During
discharge, the chemical reactions which occurred in charging are reversed. The active material (Cd) in the
negative plates gradually loses electrons and changes to cadmium hydroxide. The active material in the
positive plates gains electrons and changes to nickel hydroxide. No gassing occurs during a normal
discharge. The insolubility of the active materials and the fact that the potassium hydroxide does not
participate in the cell reaction results in the very flat Ni-Cd discharge voltage curve.
The rate at which the conversions take place is primarily determined by the external resistance (load)
introduced into the circuit in which the cell is connected. Due to its construction, the MarathonNorco cell
has an extremely low internal resistance, and its ability to deliver high currents is due to this factor.