Page 346 - Battery Reference Book

Shelf life-percentage capacity retained 3W7

4 5 7 50 25
Hourly rate

0 20 40 60 80 100 120
Percentage of rated capacity
Figure 30.45 Discharge characteristics under continuous duty of a 20-cell zinc-air battery (Courtesy of McGraw Edison)

- 3.0
-
>
0
m
:
2.5
P
- -
0
Lu 2.0
0 20 40 60 80 100 120
Percentage of rated capacity
Figure 30.46 Hc'neywell lithium-sulphur dioxide cell room temperature discharge profile as a function of load, with 2.0V cut-off (Courtesy
of Honeywell)
temperatures near to 20°C. Obviously, capacity fall-
g 100
off during storage is greater at elevated temperatures -
such as might occur in the tropics. Plots of percentage .- 80
.+
retained capacity versus shelf life at stated tempera- 260
tures are a useful way of comparing this characteristic
for various types of cell or battery. Figure 30.47, for i?
example, shows a plot of percentage retained capacity .: I-' 20
versus shelf life in months at 20°C for a 1.5V alkal- c
ine manganese dry cell when the battery is under an 0 12 24 36
ohmic load of 25 Q, i.e. a current drain of 60 mA. The Storage time at 20 "C (months)
preparation of such plots at a range of temperatures Figure 30.47 Typical capacity retention of an MN 1500 alkaline
enables the temperature coefficient of the percentage manganese cell, 25 W20"C (Courtesy of Union Carbide)
capacity retention of the cell to be calculated.
retained after 4 years' storage at 20°C. A typical
30.5.1 Silver-zinc primary batteries performance curve is shown in Figure 30.47.
The dry storage charge retention characteristics of this
batteiy are excellent at temperatures up to 52°C. 30.5.3 Mercury-zinc primary batteries

30.5,.2 Alkalline manganese primary batteries The service capacity of mercuric oxide batteries after
1 year of storage at 21°C is generally more than 90%
Alkaline manganese batteries retain their capacity for of the capacity of a fresh battery. Figure 30.48 shows
30 months without significant loss. For example, after the effect of storage time on e.m.f. at 21 and 35°C.
12 months' storage at 20°C batteries are capable of Batteries can be stored for periods of up to 3 years; it
realizing over 92% of their initial capacity. With the is not, however, good practice to store them for long
best type of cells, approximately 80% capacity is periods.