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Self-discharge processes are processes that decrease the performance of electrochemical power sources without flow of current through an external circuit (i.e., with no load connected to the positive and negative poles). Batteries that are prone to self-discharge are generally disfavored by industry, because they have a short shelf life and require regular monitoring to maintain them in a full state of charge. | Self-Discharge H Wenzl Beratung für Batterien und Energietechnik Osterode Germany and Clausthal University of Technology Clausthal-Zellerfeld Germany 2009 Elsevier B.V. All rights reserved. Definitions and Terms Self-discharge processes are processes that decrease the performance of electrochemical power sources without flow of current through an external circuit i.e. with no load connected to the positive and negative poles . Batteries that are prone to self-discharge are generally disfavored by industry because they have a short shelf life and require regular monitoring to maintain them in a full state of charge. Self-discharge also decreases the energy efficiency of the electricity storage process particularly if the power source has to be maintained in its fully charged state for long periods of time. The relevance of self-discharge reactions is therefore application specific. For primary batteries that are used to supply power to electronic devices at a low rate for many years the self-discharge rate must be very low and even after a few years of storage the capacity of the cell must still be very high and all other performance criteria should be within acceptable limits. Self-discharge is typically assessed by keeping a battery or supercapacitor in a load-free state for a fixed period of time at a specified temperature e.g. 6 months and 20-30 C for stationary lead-acid batteries according to EN 60896 or 21 days at 40 C for lead-acid starter batteries according to EN 50342 and then measuring subsequent performance. For stationary batteries the loss of capacity is used to define the self discharge rate. For starter batteries either the low-temperature voltage or cold cranking current is used. The latter is the amount of current a battery can deliver for 30 s at -18 C without dropping below a specified cutoff voltage 7.5 V . Selfdischarge processes always reduce the capacity. If the result of self-discharge reactions are for instance passivating layers the .
