Page 147 - Battery Reference Book

Alkaline manganese secondary batteries 6/5

of time, the complete dischargdcharge cycle can be
repeated many times before the battery voltage will l7 t
drop below 0.9 Vkell in any discharge period, depend-
ing on cell size. Decreasing either the discharge current
or the total ampere hour withdrawal, or both, will '61-
increase the cycle life of the battery by a signifi-
cant percentage. Conversely, if the power demands are
increased to a point where they exceed the rated battery
capacity, the cycle life will decrease more quickly than
the increase in power demand. During the early part
of its cycle life there is a very large power reserve in
the Eveready rechargeable alkaline manganese dioxide
battery. In these early cycles, the battery terminal volt-
ages may measure 1.0-1.2Vlcell after the battery has P
%
delivered its rated ampere hour capacity. This reserve 6 11 1.09 A
power can be used in situations where maximum total D J
h
.\ of discharge
1
battery life can be sacrificed for immediate power. 10
During the latter part of cycle life, there is little or no
reserve power and the terminal voltage of the battery 9
will fall to between 1 .O and 0.9 V/cell at the end of dis-
charge. Figure 6.5 shows the maximum and minimum 8 I I I 1 4 h of discharge
I
discharge voltages that the battery will reach on evenly 10 20 30 40 50
spaced cycles throughout its cycle life; the curves show Number of cycles
561 battery performance on a 9.6 52 load for 4 h.
Eveready rechargeable alkaline manganese dioxide Figure 6.5 Typical voltage performance on voltage-limit4 taper
batteries have excellent charge-retention properties. current charge: Eveready 561 rechargeable 15 V alkaline
manganese dioxide battery. (Charge and discharge conditions
The new battery is fully charged and has the charge- as for Figure 6.4.) (Courtesy of Union Carbide)
retention characteristics of a primary battery. These
characteristics also apply during the chargeldischarge
cycling of the battery. With this type of battery it is 1 Ah after three years' storage at 25°C (self-discharge
necessary to discharge it to its rated capacity before it rate 0.01% per day compared to 1% per day for
will be capable of standing any overcharge. nickel-cadmium cells). More than 100 cycles are
Rayovac supply their Renewal range of zinc-man- achieved if a regime of partial discharges is adopted.
ganese dioxide RAM cells. In the 1.8 Ah AA size the The energy density of these cells is 80 WNkg-l
voltage ranges from 1.9 V to 0.9 V at end of discharge. (220 W l~/dm-~), i.e. approximately twice the value
The 1.8 Ah initial capacity of this cell decreases to achieved for nickel-cadmium cells.