Failure occurring in the batteries is practically never a sudden affair. It generally makes itself apparent by gradual diminution of capacity that is to say, the batteries refuse to give their proper amount of current for the required time, and this state of things gradually gets worse and worse. It is nearly always due to the batteries being forced to give more current for prolonged periods than they should, and generally results from the dropping out of paste from the positive plates, or to an interference with the continuity of the paste and the conductor. In badly mounted batteries that is to say, those in which the plates are set up either without a bridge or without a sufficient bridge failure may be due to short circuiting, owing to some of the active material falling out on to the bottom of the cell, and bridging the plates across. In general, however, the failure of a well-constructed battery, within the period for which it ought to run, is due to overwork.
It is well at intervals to employ a cell-testing voltmeter to test all the different cells, as it may sometimes happen that one or two cells get into bad condition. If their voltage is low towards the end of a run the main battery will be charging them round the wrong way, and they will in consequence be injured. If the same cells persistently show low voltage, they ought to be removed and examined. Hence easily detachable connections are advisable.
The injury nearly always occurs to the positive plates. Consequently a battery that has been maltreated may practically be rendered as good as new by renewing the positive plates. As the connections, battery boxes, and negative plates are not influenced, renewal of the positive plates can generally be effected at a reasonable price.
All battery connections should be seen to every day, and if any sign of oxide or verdigris appears should be promptly removed and cleaned. They should also be kept thoroughly tight. Perhaps the proprietor of an electric vehicle would do better, if he suspects his batteries of being in an unsatisfactory condition, to get them inspected by the builder of the cells, as
