Measure battery voltage at night with no power connected, then with power connected, you should see a voltage increase.
Unless you are parked under VERY bright street lights, the solar won't be generating any power. If the street lights are causing the solar panels to generate - Yipee, you're getting something from the council for free!!
I know vehicle batteries get very cold but if used every day they don't freeze for months on end like caravan batteries. If possible try to run the engine every week for 15 mins to keep the engine battery topped up. I can charge my engine battery from my caravan side charger when stationary, but most people won't be able to do that as they will be using a split charge relay.
The freezing point of the sulphuric acid electrolyte varies with the concentration. The freezing point of the electrolyte in a discharged battery is high enough to be significant during normal winter weather, while that of a fully charged battery at 1.250 specific gravity is low enough to be safe under all weather conditions. These points are of importance in the storage and operation of battery under severe cold weather conditions.
Message - keep it charged
IanM
I was trying to be very careful this winter and have had my van on trickle charge from the mains ala campsite fashion. However, today all batteries are flat as flat. It would seem that some days ago my son had disconnected the mains lead. So - my question is, if the van's electric panel has been on for some days, though no electrics running in van, would that be enough to drain the leisure and the engine batteries? Ideas, anyone?