Vented pocket plate cells

Vented sintered plate cells are more expensive to produce than pocket plate cells and are therefore restricted mainly to applications where their mechanical integrity and resistance to shock and acceleration together with their high power density are of importance, e.g. in aircraft, helicopters, military vehicles, city buses, etc. Twenty-four volt batteries are generally used, with capacities in the range 30-60 Ah. 

In vented cells the sintered metal is cut to the final plate size and, after conduction tabs are welded, the cell is put together in a similar way to the pocket plate cells except that the separator is a thin sheet of low-resistance, small-pore plastic often with a second layer to prevent oxygen transport. These membranes may be cellophane and a non-woven polyamide respectively. 

Cell construction is mainly confined to two types, using either pocket plate electrodes (vented cells) or sintered , bonded or fibre plate electrodes (vented and sealed cells). In the former, the active materials are retained within pockets of finely perforated nickel-plated sheet steel which are interlocked to form a plate. Positive and negative plates are then interleaved with insulating spacers placed between them. In sintered plate electrodes, a porous sintered nickel mass is formed and the active materials are distributed within the pores. In sintered plate vented cells, cellulose or other membrane materials are used in combination with a woven nylon separator. In sealed or recombining cells, special nylon separators are used which permit rapid oxygen diffusion through the electrolyte layer. 

Iron-nickel oxide cells are always vented. Tubular/pocket plate electrodes are constructed as described above and are generally housed in nickel-plated steel cases. Cells with sintered plate electrodes have smaller inter-electrode spacings. They use synthetic fibre fabrics as separators, and plastic containers. 

Batteries in standby service can be maintained in a fully charged condition by a float or trickle charge similar to pocket plate batteries. The float voltage for vented sintered-plate batteries is 1.36 to 1.38 V per cell. 

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