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NICKEL METAL HYDRIDE BATTERIES - CONTINUED
Five Main Characteristics
As with Ni-Cd batteries, nickel-metal hydride batteries
have five main characteristics: charge, discharge,
storage life, cycle life and safety.
Charge characteristics
Like Ni-Cd batteries, the charge characteristics of nickel-
metal hydride batteries are affected by current, time and
temperature. The battery voltage rises when the charge
current is increased or when the temperature is low.
The charge efficiency differs depending on the current,
time, temperature and other factors.
Nickel-metal hydride batteries should be charged at a
temperature ranging from 0 C to 40 C using a constant
current of 1C or less. The charge efficiency is
particularly good at a temperature of 10 C to 30 C.
Repeated charge at high or low temperatures causes
the battery performance to deteriorate. Furthermore,
repeated overcharge should be avoided since it will
downgrade the battery performance.
Refer to the section on recommended charge methods
for details on how to charge the batteries.
Charge characteristics
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0
20
40
60
Charge Capacity (%) (Nominal Capacity Ratio)
Charge temperature characteristics at 1C charge
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0
20
40
60
Charge Capacity (%) (Nominal Capacity Ratio)
Charge
: 120%
Temperature: 20C
Model
: HHR160A
1C
0.33C
0.1C
80
100
120
140
160
Charge : 1CmA x 120%
Model
: HHR160A
0C
20C
40C
80
100
120
140
160
NICKEL METAL HYDRIDE HANDBOOK, PAGE
Charge temperature characteristics at various
charge rates
110
100
90
Charge
80
0.1C x 12h
0.33C x 4h
70
1C x 1.2h
60
Discharge
: 0.2C to 1.0V
Temperature: 20C
50
Model
: HHR160A
40
-10
0
10
Charge Temperature
Discharge characteristics
The discharge characteristics of nickel-metal hydride
batteries are affected by current, temperature, etc.,
and the discharge voltage characteristics are flat at
1.2V, which is almost the same as for Ni-Cd
batteries. The discharge voltage and discharge
efficiency decrease in proportion as the current rises
or the temperature drops. As with Ni-Cd batteries,
repeated charge and discharge of these batteries under
high discharge cut-off voltage conditions (more than 1.1V
per cell) causes a drop in the discharge voltage
(which is sometimes accompanied by a
simultaneous drop in capacity). The discharge
characteristics can be restored by charge and
discharge to a discharge end voltage of down to 1.0V
per cell.
Discharge characteristics
2.0
1.8
1.6
0.2C
1C
1.4
1.2
1.0
0.8
0.6
0
20
40
Discharge Capacity (%) (Nominal Capacity Ratio)
1C
0.33C
0.1C
20
30
40
50
60
Charge
: 1CmA x 1.2h
Temperature: 20C
Model
: HHR160A
3C
60
80
100
120
August 2000
10
70
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