I've had this OBDII dongle for a few years now and it has been very useful in identifying and clearing fault codes from my trusty, rusty FL2. I learned something new today though.
Yesterday, the car was a bit tardy in starting. Hadn't been started for 3 or 4 days and it turned over a bit slower than normal before eventually kicking into life. Ach well, I thought, the battery's getting on a bit; might have to change it soon.
Today I was trying to connect something to the home WiFi and I noticed the Tacklife WiFi was available. I'd left the dongle plugged in over a week ago and it was broadcasting on WiFi. That means the dongle must be powered up even with no key in the dock and the car double locked. Could that be the reason my battery seemed a bit flat? I don't know for sure, but it's something to look out for.

Possible, in my freelander 1 I had an insurance tracker plugged in, that was constantly powered. Although the drain would be very small. 3 to 4 days I wouldn't expect any difference so maybe the cold has tipped the battery over the edge.

Many cars have the diag port powered all the time, and yes that's probably your battery drain.

Get one of these. If the car is less than 25yds away you can check up anytime ....