Trickle charge

Trickle charging means charging a fully charged battery under no-load at a rate equal to its self-discharge rate, thus enabling the battery to remain at its fully charged level. A battery under continuous float voltage charging is said to be under float-charging.

For lead-acid batteries under no-load float charging (such as in SLI batteries), trickle charging is achieved naturally at the end-of-charge, when the lead-acid battery takes in a trickle charge to keep itself fully charged. The trickle charging then equals the energy expended by the lead-acid battery in splitting the water in the electrolyte into hydrogen and oxygen gases. Other technologies, such as the lithium-ion battery technology, are highly intolerant to over-charging, and cannot be float-charged without an external battery management system.

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Wikipedia