Charging aux AGM battery when plugged in

[goffro]

Hey gang. 2002 Eurovan Transporter T4 here! We bought an absorbed glass mat (AGM) battery as a replacement aux battery.

The operator's manual says the following about charging the aux battery when it's plugged into 110 volt:

"The converter in this vehicle has a special electronic charger section which also charges the coach battery while the shoreline is plugged into a 110-volt source. The electronic charger constantly monitors and adjusts the rate of charge so the battery is not undercharged or overcharged -- the two major causes of battery deterioration and failure.

"If the coach battery has been extremely discharged, it will accept charge at a relatively high amperage rate. If it is only slightly discharged, it will charge at a lower amperage rate. The rate of charge will decrease as the battery reaches full charge. Active charging will not resume until the battery again falls below full charge. The converter will not overcharge the battery. If your storage battery does not charge as described above, it is possible the battery is defective.

I don't know that much about battery technology, but I'm a little concerned that the Van's built-in charger is designed to charge the (stock) deep cycle lead battery, but now we are using a different battery technology. Might it make sense to look into replacing the stock charging section with one that is optimized to charge AGM battery?

[e&m_ghia]

A guy I work with used to do research in battery chemistry. But not for lead-acid batteries.

When I idly asked about the built-in charger for our 97 EVC coach battery (recently replaced with an AGM), he didn't think that the charger (basically rectified but unfiltered power) was the best thing for the longevity of the battery. It basically recharges with lots of really short, shallow charge-discharge cycles.

But he had no idea how bad it might be, or if the effect would even be perceptible. That answer would require research, of course.

At some point, I'd be inclined replace the charger on ours. But not this season. I'll wait for some other reason, to tear into that cabinet.