The capacity increases with the temperature, being about one per cent. for each degree Fahr. increase in temperature.
Battery capacity depends on the size and number of plates; the quantity of active material present, and the quantity of electrolyte.
For an eight hour rate of discharge and 60 degrees temperature, the capacity of American batteries varies from 40 to 60 ampere hours per square foot of positive plate surface ( = 2 × number of positive plates in parallel × length × breadth).
The following table gives the variation of capacity for different rates of discharge:
| Discharge rate | Per cent of capacity at 8 hour rate | |
|---|---|---|
| Plante | Faure | |
| 8 hour | 100% | 100% |
| 6 hour | 96% | 96% |
| 4 hour | 80% | 88% |
| 2 hour | 61% | 70% |
| 1 hour | 56% | 48% |
Fig. 1,136.—"Exide" connector puller for removing connectors.
Ques. How may the capacity of a battery be increased?
Ans. By mixing organic materials with the lead oxide, but any such mixture is always accompanied by a rapid deterioration of the plates.