Sudden unexplained drop in SOC?

I’ve owned my 2014 ED for just over a year now and there have been a handful of times when the state of charge drops 10-20% while the car is parked for a few hours. The first time it happened, I thought I was just imagining it. It happened again today and I’m positive it is real. It was at 40% SOC when I parked at work in the morning. When I got In to go home seven hours later, the SOC had dropped to 30%. Any thoughts on what would cause this to happen? I am still on the original 12V battery.