I always rely on a DC MULTIMETER across the battery main 12VDC switch. If the battery bank is fully charged it will read 12.6-7VDC when not connected to shore power or generator.
When I plug the trailer into shore power the DC VOLTAGE at the battery switch will jump up to 13.6VDC or whatever charge mode the converter is in if it is a SMART MODE charger type. when my battery is reduced down to its 50% charge state my smart mode converter/charger when connected to shore power starts out in 14.4VDC for a couple of hours, then drops back to 13.6VDC for an additional hour, and finally then drops to 13.2VDC when no load is detected. This is when my batteries are at 90% charge. If I leave it all running for a total of around 12 hours then the battery bank will achieve a 100% charge state.
If I don't see this DC VOLTAGE jump then I know for some reason the batteries are not connected to the converter/charger unit or the converter/unit is not coming on etc...
If it starts up in 14.4VDC mode but really draws alot of current (more than 17AMPS per battery) then I know one of the batteries must have a dead cell in it and needs to corrected before I can continue using the batteries.
I use a manual BATTERY MONITOR panel that monitors my two battery banks DC VOLTAGE level and another DC CURRENT meter that will monitor what the load DC CURRENT when not connected to SHORE POWER. When I am connected to shore power then this DC CURRENT METER will show how many amps is being demanded by the batteries when they are being re-charged.
Really helps in knowing what is happening at all times when you have to depend so much on the batteries to make it through the night when you need them...
This is how I manage my battery bank...
Botton line is to learn what to look for and then perhaps you won't end up with a big surprise using your batteries way back off the road somewhere when you really need them to work for you.
Roy ken
