CTEK Chargers

How old is the auxiliary battery and is it a deep cycle? Could be adding to the problem. Is the auxiliary fitted in the bonnet space, as deep cycle batteries don't like being hot?
We had significant problems with our van deep cycle battery which was being "charged" by the Jayco 240V/12V "charger" in the van; the charger merely floated the battery at a constant voltage which would stuff it in fairly short order.
I fitted a D250S (without Smartpass) to our van a couple of years ago plus a 130W solar panel. The D250S charges our 110 Ah deep cycle battery from the solar or from 12v from the car (when towing) or using the 12V from the Jayco system when plugged into 240V. We run a 60litre Engel as a fridge plus lights plus occasionally a 200w inverter in the van. Despite camping for several nights in a row without 240V power and without running the car, the battery has never been down by more than 20% in the morning, and usually if it's sunny, using only the horizontal solar panel on the roof plus the MPPT regulator in the CTek, the battery is indicating fully charged by 10am. Very happy with the CTek purchase. If you are only running the vehicle for a short time for recharging purposes, then consider the Smartpass, as it will allow charging rates above 20A from the vehicle alternator.

It doesn't matter what you install, if you don't do enough kilometers to recharge the battery. Batteries take time to charge, by charging straight off the alternator you will replace the bulk charge sooner, the smartpass and DCDC charger will give you the best of both worlds but you still need to drive long enough to charge the batteries, you may be better off just using a good mains charger when the cars garaged.