What I do is to measure across the Battery terminal with my DC VOLT METER and read the Battery DC Voltage. It usually reads 12.5-6VDC...
Then I connect my Trailer 30A Cable to either a shore power 120VAC Connection or my 2KW Generator set 120VAC connection. The reading on my battery terminals will jump up to 14.4VDC telling me the battery is demanding a charge from the converter charging setup...
When I am camping I do this every morning... When parked at home base I will do this test at least once a week...
When my battery terminal DC Voltage reading gets down to the 12.0VDC reading which is approximately the 50% Charge state then I will do a full 100 percent charge procedure... My on-board converter PD9260C charger goes thru the smart mode charging modes being 14.4VDC, 13.6VDC and 13.2VDC and can provide up to 60AMPS DC charging demands.
My original Converter Charger would only produce 13.6VDC at 30AMPS DC Current which did not do well keeping my Trailer batteries properly charged. Also having the original DC Converter 13.6VDC on-line for long times would also boil out my battery fluids. I lost one of my 12VDC Batteries not catching this in time... That was when I changed out the original ELIXIR Industries ELX-30 converter/Charger for the Progressive Dynamics PD9260C 60AMP Model converter/charger, Never had a Battery issue with my three installed 12VDC Batteries after doing that...
Roy Ken