Something draining battery

When things get cold they contract. I suspect you have a switch that needs replacing. Many years ago I had a car that when it got really cold outside the horn would start blaring. I replaced the horn switch in the steering wheel and that fixed it. What was happening was the cold caused the switch to contract and make contact like someone was pressing the horn button. I'm thinking the same thing is going on with your vehicle. Only something less obvious than the horn blaring at 3am is turning on and draining the battery. Possibly the interior lights or maybe the blower motor for the heater. I'd suggest waiting until it's cold outside and walk around the vehicle. Look for any lights on and listen for anything running. Once you determine what it is, you can replace the offending switch. Hope that helps! Jim