Like the charging rates, the currents are usually specified only for the bulk charge stage. The charge current required for a given charging rate is calculated as follows:Ĭurrent = rate x battery capacity Current (A)īecause amperes are key to AGM charging practice, it is important that you can translate the C-rates into amperes and back. Let us take a few application examples: Charging a typical 60Ah car battery at the normal charging rate of 0.1C takes a current of 0.1C x 60Ah = 6A. Fast charging a larger 100Ah AGM battery at 0.3C takes a current of 0.3C x 100Ah = 30A. The standard charging rate 0.1C to current conversion is very easy to remember: AGM charging current = battery amp-hours / 10. The maximum current you should use to charge an AGM battery is, in most cases, the current that produces a 0.3C charging rate. This is the max rate recommended by most AGM battery manufacturers. The maximum charging current depends on the battery size, and can be obtained using the formula above. For a rough estimate of the max current in amps, divide the battery amp-hours by 4: a 60Ah battery takes 15A, a 100Ah battery 25A, and a 200Ah battery 50A. With larger-capacity AGM batteries, the maximum recommended charging current cannot be sourced by typical battery chargers, and the charger capacity will limit your currents. The charging rate of an AGM battery is controlled by selecting the appropriate current setting in your charger. Most battery chargers allow you to select the bulk charge current from only a few options.

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