to the operator is measured in terms of the 

 number of charge and discharge cycles it can 

 undergo and still be recharged to its near 

 rated capacity (amp-hr). High rated batteries 

 (delivering large current drains for periods 

 of several minutes to 1 hour) have a shorter 

 wet life and cycle life than low or medium 

 rated batteries (discharge at rates from 1 to 

 10 hours). Under atmospheric conditions the 

 shelf life and cycle life characteristics paral- 

 lel those shown in Table 7.4. 



A great deal of recent battery studies con- 

 centrate on silver-zinc cells (11, 12, 13, 14) 

 and provide both laboratory and field data 

 regarding their cyclic longevity. Again, 

 though lead-acid batteries have been used 

 for years, there are no known reports regard- 

 ing their cycling characteristics in the ocean. 

 Hence, the following data apply only to sil- 

 ver-zinc cells. 



In laboratoi-y experiments Funao et al. 

 repeatedly cycled two oil-filled batteries 

 (placed in a "soft" container and surrounded 

 by oil) to 600 kg/cm^ (8,532 psi) and dis- 

 charged them at 150 amp for 2 hours. Dis- 

 charge was followed by a 35-amp charge to 

 2.05 volts and every 10 cycles the battery 

 was discharged to 1.0 volt and measured. A 

 comparison of the data between the pressur- 

 ized battery and a similar battery not sub- 

 ject to pressure (Fig. 7.5) shows that dis- 

 charging under pressure delays the rate of 

 capacity decrease. The cause of expiration 

 was short circuits through the separators of 

 both batteries. Work (11) reached similar 

 conclusions after cycling identical ten-cell 

 250-amp-hr batteries for 2 years in simulated 

 deep-ocean conditions. He found the rate of 

 capacity loss to be the same as that of a 

 similar battery operation at atmospheric 

 pressure for the same period. Momsen and 

 Clerici (13) reported the results of silver-zinc 

 cell use on the Deep Submergence Vehicle 

 TRIESTE II and concluded that this type of 

 battery is entirely suitable so long as usage 

 is maximum. 



Charging 



Extensive testing demonstrated that 

 charge reception is reduced slightly when 

 silver-zinc battery temperatures are at 32°F 

 or less (13). Whereas charging (and discharg- 

 ing) are heat generating processes, the low 



heat transfer coefficient for the cells tends to 

 keep them warm. Work (14) discussed heat 

 transfer within batteries and pointed out 

 that a number of cells packed tightly to- 

 gether can dissipate little heat. Rapid cy- 

 cling causes the temperature of the center 

 cells to rise appreciably above that of the 

 outside cells and results in an unbalanced 

 condition. To rebalance the batteries two 

 approaches are taken: 1) The entire battery 

 is charged and then floated at a low rate for 

 a few days, or 2) individual cells are charged 

 or discharged at a low rate through the 

 voltage monitor system harness. 



Spill Angle 



The normal orientation of wet cell batter- 

 ies is upright; most are equipped with spill- 

 proof devices and can withstand up to 30- 

 degree tilting without ill effects. Work (14) 

 reported that cells are under design with 

 angles of 45 to 60 degrees from the vertical 

 as a goal. The same report relates an inci- 

 dent where a surfaced vehicle rolled as much 

 as 90 degrees. A 90-degree roll is, to say the 

 least, quite unusual, and one might find it 

 more advisable to reconsider the vehicle's 

 stability rather than designing batteries to 

 withstand roll angles of this magnitude. 



DISCHARGE CURRENT 150 amp 

 CHARGE CURRENT 35 amp 



LIFE CYCLE 



Fig. 7 5 Life characteristics of silver-zinc cell. [From Ref (12)] 



323 



