b. FUNCTIONAL DESCRIPTION.
The battery when charged, has positive electrodes of silver oxide and negative electrodes of metallic
zinc. During discharge the positive plates are reduced to silver while the negative plates are Oxidized
to zinc-oxide. Charging the battery reverses this process (returns It to the charged state). The
electrolyte acts as a medium for the exchange of Oxygen, and is also the current carrier within the cell.
In an alkaline cell, unlike a lead-acid cell, the electrolyte does not take part in the chemical trans-
formations. Therefore, its specific gravity does not change with state of charge of the cell. This
then, makes a hydrometer useless with the BB-451/U Silver-Zinc Storage Battery.
(1) Intended Use. The BB-451/U is designed to provide a lightweight power source to meet the high-
current demands for man-pack radios such as the AN/PRC-41 and the AN/ PRC-47.
(2) Limitations. The following limitations apply to this battery.
(a) Heavy Discharge Sensi tivity. Even though the BB-451/U is rated at 25 AH at 24 volts dc for radio
receiving and transmitting applications, it is recommended that it not be discharged more than 20 AH
per cycle, since a deeper discharge will materially shorten the battery life.
(b) Low Temperature Sensitivity. The performance of the battery is seriously affected by low tem-
peratures. At temperatures below approximately -35°C (-31°F) the battery effectively ceases to
operate
(c) High Temperature Sensltivlty. The performance of the battery la seriously affected by very
high temperatures. At temperatures above 100°F (37.8°C). the cycle life and wet life are greatly
reduced (see Table 1-2.).
(c)
Sensitivity to OverFilling. Both the silver and zinc plates of the battery are soluble in the
electrolyte, therefore, the instructions on filling should be carefully followed (see paragraph 1-4
"Servicing").
(d)
Sensitivity to OverCharging. The battery will not accept excessive current during overcharge,
but rather, this current will cause the generation of hydrogen and oxygen, and will be of no aid to
charging the battery.
WARNING
THE BB-451/U IS A SILVER-ZINC BATTERY UTILIZING AN ALKALINE ELECTROLYTE
OF 40% POTASSIUM HYDROXIDE (KOH). DO NOT INSERT SULFURIC ACID (H
2
SO
4
) USED IN
LEAD-ACID BATTERIES, AS ACID WILL REACT VIOLENTLY WITH THE ALKALINE
ELECTROLYTE CAUSING PERMANENT DAMAGE TO THE BATTERY AND POSSIBLE
INJURY TO THE USER
TABLE 1-2. BATTERY PERFORMANCE AT VARIOUS
TEMPERATURES
Temp (°F>
Cycle Life*
Wet Life (Months )**
-13
20
12
0
20
12
32
25
12
40
30
16
75
30
18
90
25
18
100
20
12
120
10
2
140
10
1
* Cycle Life: The number of charge/discharge cycles the battery
experiences.
'* Wet Life: Useful life of activated battery.
