AGM Battery Discussion-Discharge/Charge Cycles

IMO since the charger is only used when alongside, there is no need to take it to sea and get salt water all over it. Alongside, it ought to be possible to keep it in the boat under cover out of the rain. (and under lock and key) Before sailing, put the charger in your RV.

Standard deck mount converters that have 120v plug- ins can be "portable." You just use output wires with battery clamps on them instead of ring terminals if you don't want to do any work connecting/disconnecting every time.