After 3 days waiting, the Skoda authorized service gave the diagnosis. Apparently one of the BCM (battery control module) module firmware was out of date and it caused the 12V battery drain itself even when the car is in off mode! As I had service insurace, the towing (twice in a day), jump starting etc. was covered, but for some reason upgrading of the BCM firmware was not. As car had only been inspected by the same service only 2 weeks ago, they accepted the diagnosis cost, so I only had to pay 120 eur for the upgrade. That's a number I guess I can give with. Though I admit, I lost confidence in the car. I mean only a month ago, I drove this car 7500 km across Europe, believing that it's trustworthy. But a simple bug could have made my trip horribly wrong. I am fortunate that I drove around 750 km/day so the percupiration saved me. By the way, the service also confirmed that the only way to recharge the 12V battery is by percupiration process. As a back up solution I've decided to buy a small jump starter pack, which is the size of a VHS tape (youngsters won't know what that is !) generally a small box packed with batteries, capable of supporting 800A/1000A, just good enough to start the car up. It's quite nifty and handy. It's good to keep one charged all times in the boot. It costs around 30-50 eur for a decent one from Amazon. Anyway, I'm grateful for all of your help. Summary: Reason: BCM Fault Solution: BCM firmware upgrade and recupirate until the battery is recharged. Risk: It can happen to anyone with a PHEV or EV. Carry a small jumpstarter pack.