A battery tester is an electronic device intended for testing the state of an electric battery, going from a simple device for testing the charge actually present in the cells and/or its voltage output, to a more comprehensive testing of the battery's condition, namely its capacity for accumulating charge and any possible flaws affecting the battery's performance and security.

The most simple battery tester is a DC ammeter, that indicates the battery's charge rate.^[1] DC voltmeters can be used to estimate the charge rate of a battery, provided that its nominal voltage is known.^[2]

There are many types of integrated battery testers, each one corresponding to a specific condition testing procedure, according to the type of battery being tested, such as the “421” test for lead-acid vehicle batteries.^[3] Their common principle is based on the empirical fact that after having applied a given current for a given number of seconds to the battery, the resulting voltage output is related to the battery's overall condition, when compared to a healthy battery's output.^[4]

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