electrical fault?

my batterys not charging when driving or on electric hook up. they saying that they are fully charged on electric panel inside campervan. but the engine wont turn over. when batteries charged in house it will start the engine. they are both new battries but they seem to be losing there charge overnight. can.t understand why they wont charge on electric hook up. checked that nothing has been left on nothing has. my motorhome is a talbot express 2l petrol 1988