The actual ageing process results in a gradual reduction in capacity over time. Lifetimes of 500 to 1200 cycles are typical. An obvious example is the Depth of Discharge (see below) which is a simple reciprocal mathematical relationship, but there are many more complex factors which can also influence performance. Key factors affecting cycle life are time t and the number N of charge-discharge cycles completed. Battery Cycle Life is defined as the number of complete charge - discharge cycles a battery can perform before its nominal capacity falls below 80% of its initial rated capacity.Battery Shelf Life like calendar life is the time an inactive battery can be stored before it becomes unusable, usually considered as having only 80% of its initial capacity.The graph below illustrates these effects. Similarly the t 1/2 (or √t ) relationship represents how the battery internal resistance also increases with time t. A rule of thumb derived from the Arrhenius Law describes how the rate at which a chemical reaction proceeds, doubles for every 10 degrees rise in temperature, in this case it applies to the rate at which the slow deterioration of the active chemicals increases. There are two key factors influencing calendar life, namely temperature and time, and empirical evidence shows that these effects can be represented by two relatively simple mathematical dependencies. Battery Calendar Life is the elapsed time before a battery becomes unusable whether it is in active use or inactive.Performance also deteriorates with usage and this is known as "cycle fade" Ways of improving battery life and hence reliability are also considered below.īattery performance deteriorates over time whether the battery is used or not. This page describes the factors influencing battery life.īattery life can usually only be extended by preventing or reducing the cause of the unwanted parasitic chemical effects which occur in the cells. These changes are usually irreversible and they affect the electrical performance of the cell. That batteries have a finite life is due to occurrence of the unwanted chemical or physical changes to, or the loss of, the active materials of which they are made. Overestimate the battery lifetime and you could lose a fortune. Offer too low a warranty period and you won't sell any batteries/products.
Woodbank does not monitor or record these emailsįor product designers, an understanding of the factors affecting battery life is vitally important for managing both product performance and warranty liabilities particularly with high cost, high power batteries.
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