On the older trailers ,make sure the tv 12 volt
battery source is from a key on switched solenoid ,(cole hersey) the brand ,a continuouse duty solenoid ,
for this type of application .That way when the tv is running power is charging the coach battery ,but tv key off the batteries do not drain the tv battery .This will apply to newer coaches also and you get the maximum
voltage from the alternator to the coach battery.Do not use the blue isolators ,they take away 1 full volt to operate ,meaning you get 13.50
volts instead of 14.50 or so ,big difference.