The converter charger come into play when the trailer is plugged into a 120VAC connection. It's purpose to power the 12 VDC system while connected to shore power. The secondary thing the converter does is charge the battery
, which is used when NOT connected to shore power.
The biggest concern for older converters is "over charging" the battery
. Over charging boils the fluid out the battery
thus destroying the battery. It's not a problem as long as you keep filling the battery with distilled water and don't let it get low enough to expose the plates.
I have eliminated any problems with a converter by eliminating the converter. When at home I keep a Battery Minder connected which keeps the battery fully charged and does a desulfating operation at intervals. When camping for more that 4 days I have a 65 watt solar panel
that charges the battery. The battery gets charged another way, when under tow the tow vehicle keeps the battery charged.
I hope this helps in some way.