SEALED LEAD-ACID BATTERIES （3）

Published:2011/8/8 21:04:00 Author:Phyllis From:SeekIC

Battery life

The life of the battery depends to a great extent on the depth of discharge, expressed as a percentage of the nominal capacity. Figure 5 gives an idea of the effect of cyclic operation on battery life. To maximise the number of useful cycles it is best to choose a battery with a larger capacity so that the depth of discharge is reduced.





Although discharge depth is the main factor, temperature also has an effect on life. Temperatures above 50 CC should be avoided, and below -15 °C there is a significant drop in capacity. Charging at too high a voltage, or for too long, will damage the battery.

Temperature and charging voltage are the main factors affecting life in continuously charged operation.

Figure 6 illustrates typical performance in this case, where 60 % of the battery’s capacity still remains available after 5 years’ use. The 60 % level is considered to mark the end of the useful life of the battery in industrial applications.




In addition to the factors mentioned above, the construction of the battery also affects its life. For example, in standby operation the small charge current that continuously flows results in the plates gradually becoming thinner and thinner. Batteries with sturdier plates last considerably longer in such use. There are also batteries available that are optimized for cycle life. Exact specifications for the various ranges can be found on the manufacturers’ websites (see list).

Not recharging the battery after a deep discharge also has a negative effect. Sealed lead-acid batteries should not be left in a deeply-discharged state for more than a few days, and should be recharged as soon as possible. The deep discharge capability of a battery indicates whether (and how quickly) it will accept charge again after being left discharged for a long period. Modern AGM-type batteries accept charging relatively quickly after a month in a deeply-discharged state and subsequently return to their normal charging characteristics. To avoid the possibility of leaving the batteries discharged for a long time, they should be stored in the charged state. Recharging is recommended when the open-circuit voltage reaches 2.1V per cell, which corresponds to a selfdischarge to about 50 % of the nominal capacity. A healthy battery at room temperature will discharge so slowly that this value will only be reached after about 18 months. At 30 CC it will take around 9 months to reach half capacity, and at 40 :C, around 4.5 months. At lower temperatures (down to -15 :C) charge is lost even more slowly than at room temperature. The low self-discharge and associated long storage life, along with long life in standby operation, are the most important advantages of sealed lead-acid batteries over other battery technologies.

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