Nautilus battery charge question

AGMs typical need around 14.2 to 14.4 volts when charging (at ~70-75F room temperature). What voltage is the battery when it is making noise?

Generally, you don't want to hold 14.x volts "forever". The voltage should be dropped back to float voltage of somewhere around 13.2 to 13.8 volts (check battery mfg. manual for charging recommendations) after about 2-6 hours of "absorb" charging (battery voltage held at ~14.4 volts--If battery is only slightly discharged, closer to 2 hours, if battery is deeply discharged--to 50% or less state of charge, then ~6 hours).

Ideally, the change from charging to float voltage would be when the battery drops to less than ~1% rate of charge in absorb (i.e., 100 AH battery, when charging current falls to less than 1.0 amps).

Gurgling in AGM batteries is typically a sign of too high of charging voltage. And batteries will eventually vent (expel hydrogen and oxygen gasses through pressure relief caps) and you cannot restore lost water. Also the gurgling/overcharging can overheat the batteries and catalyst (if present) used to recombind the H+O gasses. The catalysts only have a limited life before they fail (more gassing, using up catalyst life).

-Bill

That is too high of charging voltage for AGM (again, check battery manual to be sure).

And once the battery is charged, either disconnect the charger (AGM batteries can go 3-6 months between charging in cooler weather and if good shape)... Or a much lower float voltage (~13.2 to 13.6 volts) for long term charging/storage.

-Bill