b) Operate at ambient deep-sea pressure 

 and thereby conserve pressure hull 

 weight. 



c) No moving parts preclude generation of 

 noise or vibration. 



d) Operate at temperatures well below to 

 well above those encountered within the 

 sea. 



e) Highly reliable, and failure occurs one 

 cell at a time such that battery opera- 

 tion may continue with only slightly 

 diminished output. 



f) Available commercially in a large vari- 

 ety of types, sizes and configurations, 

 and, for the most part, developmental 

 costs have already been paid. 



Disadvantages: 



a) Energy densities (energy per unit 

 weight) and specific energies (energy 

 per unit volume) are low. 



b) Designed for operation at power levels 

 of not more than a few tens of watts per 

 pound and a few kilowatts per cubic foot 

 (silver-zinc cells are an exception). 



The report concludes that, among the var- 

 ious conventional batteries available, silver- 

 zinc batteries appear most attractive for un- 

 dersea application. It also presents a sum- 

 mary of secondary battery characteristics 

 which is shown in Table 7.2. An analysis of 

 Table 7.2 reveals that silver-zinc cells 

 achieve the highest energy density (watt 

 hours/lb) and lead-acid the lowest with 



nickel-cadmium somewhat in between. Con- 

 versely, initial costs are in the reverse order. 

 Penzias and Goodman (6) point out that 

 there is significant salvage value, however, 

 in the silver of a silver-zinc cell while the 

 lead in a lead-acid battery is hardly worth 

 recovering. 



Discharge Rate and Temperature 



According to Cohn and Wetch (1), most 

 battery manufacturers define standard con- 

 ditions as room temperature and low dis- 

 charge, and Howard (7) standardizes this 

 condition as a 5-hour discharge at 80°F. Volt- 

 age profiles of various secondary cells are 

 shown in Figure 7.3 and clearly demonstrate 

 the steady output of silver-zinc and nickel- 

 cadmium cells. Curves presented by Kisinger 

 (8) show that the highest energy per pound 

 from secondary batteries (lead-acid; silver- 

 zinc) is obtained at slow discharge rates. In 

 short, to realize the most energy, batteries 

 should be used under load conditions which 

 will keep the drain on them to a minimum. 

 Conversely, of course, a high discharge rate 

 reduces the total amount of energy that can 

 be taken from a battery. 



In general, as temperature decreases the 

 withdrawal of current becomes more difficult 

 because the increasing viscosity of the elec- 

 trolyte hinders the passage of reactants and 

 products to and from electrodes (9). High 

 temperatures are only a problem if they are 



TABLE 7.2 SUMMARY OF SECONDARY BATTERY CHARACTERISTICS [FROM REF. (5)] 



Type 



Anode Cathode Electrolyte 



Theorel- Maximum 



Open Typical ical Actual energy power 



circuit operating energy density density Opera Typical 



Temp. voltage voltage density (W/ (W/ Cost* ting no. of 



'F IV) IVI (Wh/lbl (Wh/lb) (Wh/ln ') lb) in.') ($/kWh) Life cycles Remarks 



Conventional 

 Lead-acid Pb 



PbO, H,SOj 



-40-140 2.2 T721 



80 116 5 20 04 1 2 15 30 1 2 



09(601 2 14yr 1500 conventional lead 



storage cell; presently 

 used for submarines, 

 automobiles, etc. 



-40-140 1,36 1,01,3 



0140 1.8 13-1.6 



105 12 15 0710 15 15 0211700) 4 6 yr 1000 available as completely 



2000 sealed cell 



205 30-80+ 18 5,6 170 7.2 8.40(800) 6 18 mo 10200 high capacity and very 



high drain rales: low 

 cycle life; expensive 



•First value is cost/kWh of energy drawn from battery during anticipated cycle life. Bracketed value is initial cost. 



320 



