Originally Posted by chlinthi
There is a solar system on the trailer which has not caused any issues in the past, but i figure it is worth noting for any diagnosis help anyone can provide. I did measure the 12V terminals on the backside of the solar charge converter/controller and it also measured 12.4V.
What solar package do you have? Does it have a solar charge controller or do the solar panels go directly to the batteries? If they go directly to the batteries with no solar charge controller, there may not be a blocking diode in the panels, so when the sun goes down at night the batteries discharge the batteries... Start with disconnecting the solar (will not hurt anything) and test your batteries, this will isolate on part of the electrical system.
Also as mentioned in an earlier post check your connections to insure that are CLEAN (wire battery cleaning brush is best),spray with battery terminal protective spray and make sure they are tight. Also check the water level of the battery cells.