If the voltage is high going into the isolator and you are not seeing an increase in voltage then the isolator could be at fault.
Rv battery not charging from alternator.
If so then there is a chance that there is some sort of problem with the charging system.
If you find the lead from the alternator to the battery isolator i would see what the voltage is if it is low the alternator may not be putting out the correct voltage and that should be bench tested.
We received a question from an rv repair club member asking why their rv battery wasn t holding any juice after a full charging cycle.
Perhaps the new battery is not being adequately charged by the charging system of the truck.
The distance between the vehicle battery alternator and the camper battery is simply too far to fully charge a trailer battery from a depleted state.
One of the most popular ways of charging a 12 volt battery is by using a vehicle s alternator.
In fact if you run too many appliances you may find that your battery doesn t receive enough power to charge at all.
Your rig is on fire and you ve got to put it out.
If the vehicle is in off state expect both the batteries to get disconnect and voltage to obtain its pre set level.
The most you can do is provide a maintenance charge to prevent your trailer battery from being doa at the campsite and even this will only charge your battery to about 80.
This is how vehicles charge their own 12 volt batteries and it is often how motorhome house batteries are charged.
While your trailer umbilical cord does have a charge wire in the connector typically the size of the wire is quite small.
Not a bad idea but if you re not properly equipped you ll find that you can charge like mad and not seem to make headway.
House battery charging from the alternator is the norm the exception is a few high line coaches with oem install large battery banks and auto start generator systems too many amps needed if the batteries are low such as travel supreme electric coaches with residential fridge electric top heat etc.
While the problem of an rv battery not charging typically stems back to one common issue there are a handful of other possibilities.
Think of it this way.
It might be worth it to check out the battery and charging system alternator voltage regulator charging solenoid etc.