Follow best practices for charging AGM batteries

May 2, 2013
It's a well known "tip" that if you don't have a battery charger that can charge glassmat (AGM) batteries, you simply just put a standard charger on a low amperage setting and make sure the battery does not get too hot.

It's a well known "tip" that if you don't have a battery charger that can charge glassmat (AGM) batteries, you simply just put a standard charger on a low amperage setting and make sure the battery does not get too hot.

Why doesn't this always work? An AGM-capable charger will monitor battery voltage and supply just enough juice in order to prevent doing long-term damage to the battery.

"We have several diagnostic chargers, a phrase we coined, that work with AGM batteries and continuously monitor battery condition during the charge, shutting off automatically once it reaches optimum charge," says Dan Cox, technical support manager of Midtronics. "The battery is not overheated or overcharged, reducing the potential for damage and customer wait time."

Diagnostic chargers also can diagnose the battery by refusing to charge it and indicating it's time for a new one.

Always be sure to properly charge and replace AGM batteries, as not doing so can set DTCs and compromise your repair. For example, putting a standard lead-acid battery in a Prius will set a "triangle of doom" MIL on the instrument cluster. Furthermore, Hondas take a regular lead-acid battery, not an AGM. This is when an information system, such as Inspection Connection, can be a major help, especially when the B-tech in the shop swaps batteries but otherwise knows nothing about hybrid vehicles.

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