Page 367 - Battery Reference Book

31/16 Secondary batteries
t- Silvercel 21-300 A h models
2.0
1.81 \'
I \\

"9 0 C 2C Discharge rate 4C 5C 6C
I
I
I
I
I
I
3C
0 5 10 15 20 (a)
Discharge rate (A)
- 305 - Silvercel 21 - 300 A h models
Figure 31.41 Mid-point voltage delivered as a function of dis-
.
charge rate and temperature for a General Electric D cell charged c)
E 244-
-u
at 2.45V at 23°C for 16h, discharged to 1.4V at 23°C (Courtesy
of General Electric) f
183- X.)
>
+- .-
per unit weight (Figure 31.42(a)) and energy per unit -0
E 122-
volume (Figure 3 1.42(b)) for silver-zinc batteries in >
the 0.1 and 300Ah capacity range. The distinct $ 6 1 - - 7
improvement in the energy per unit weight or volume w I I I 1 I
of silver-zinc over nickel-cadmium, nickel-iron
and lead-acid battery systems is very apparent.
Figure 31.43 shows the effect of temperature on the
energy per unit weight available from silver-cadmium
batteries when discharged at various rates. The energy
available starts to decrease as the cell temperature
approaches - 18°C.
31 .I3 Self-discharge characteristics
and shelf life
100 -
When fully charged batteries are stored by suppliers -
or in the stores of the user then, depending on the 90
type and characteristics of the battery and other fac- Y 80- 10 h rate
tors such as storage time and temperature, the batteries L 70-
will undergo a gradual process of self-discharge. The
result is that when these batteries are called into service
they will not have the design ampere hour capacity that
would be expected of a newly manufactured battery.
Usually, the full capacity can be restored to the battery
by subjecting it to a process of acclimatization whereby
it is given a few charge/discharge cycles under con- 10 ;-
trolled conditions. After a few such cycles the full
capacity of the battery is usually restored. In some -40 -30 -20 -IO 0 10 20 30
circumstances, batteries in store are given a periodic Temperature ("C)
topping up charge to restore their full capacity, which Figure 31.43 Effect of temperature on energy per unit weight
is then available when the batteries are brought into of Silcad YS-18 rechargeable silver-cadmium cells (discharged
service. without heaters) (Courtesy of Yardney)