Charging silver-oxide batteries

FIGURE 25.24 Charge-discharge characteristics of nominal 140-Ah iron/silver oxide battery. From Ref. 20.)... 

The charge retention of the activated and charged silver oxide cells is better than that of most secondary batteries, with retention of 85% of charge after 3 months storage at 20°C. 

Aside from normal capacity loss due to extended wet or cycle life, dry-charged zinc-silver oxide batteries may exhibit a one-time deviation in capacity performance (typically less than 20% of initial capacity) during the second cycle discharge called second cycle syndrome. The cause of this deviation is unknown but is generally recognized by the user community. 

Freshly assembled cells are subjected to a series of formation cycles in order to activate the system. Cells are often sold in a charged but dry state, in which case the formation process is performed before the final cell assembly. Dry charged batteries can be stored indefinitely. Cells containing electrolyte should be stored in the completely discharged state since dissolution of silver oxide is then avoided. 

It must be emphasized that the most appropriate charging regime is very dependent on the cell system under consideration. Some are tolerant to a considerable amount of overcharging (e.g. nickel-cadmium batteries), while for others, such as zinc-silver oxide and most lithium secondary cells, overcharging can result in permanent damage to the cell. Sealed battery systems require special care float charging should not be used and trickle charge rates should be strictly limited to the manufacturer s recommended values, since otherwise excessive cell temperatures or thermal runaway can result. 

Dry-charged battery — Batteries that are shipped and stored in the charged state, but dry and free of electrolyte. Under such conditions the batteries exhibit very long shelf life, and can be rapidly activated by introducing the electrolyte upon demand. Silver-oxide based bat-... 

Forms of this battery type range from those used in hearing aids, watches, and cameras to those used as portable power sources in space vehicles. The cathode/anode and electrolyte system is similar to that for the alkaline ceU, except the Mn 02 cathode material is replaced with much more expensive silver oxide (Ag O). However, it has high stability, a long shelf life, and a large charge density with a stable voltage (about 1.8 V). 

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