You shouldn't loose 50% of your battery charge in a week and a half. 50% loss over a few months, possibly, but not a week and a half. I'm assuming you're looking at the SOC (State of Charge) estimate on the driver's information area behind the steering wheel.
The Clarity will use some battery to maintain battery temperatures - was it really cold (below freezing) while the car was sitting? This will cause the car to run the resistive heaters to keep the battery warm while it's really full. Once the battery runs down some it's won't get damaged by the cold temperatures (full LiON batteries are easily damaged by freezing).
Something else to check is for a parasitic draw? This would cause the 12v battery to be discharged. The Clarity maintains the 12v battery charge using the main traction battery as a charging source. If the 12v dies you can't start the car's computers, which means the car won't start.
2018 Honda Clarity Touring PHEV - Forest Green w/Tan interior (wife's car)
2017 Volt LT - Heather Gray; black bow ties, Charcoal VoltShelf
2012 Cruze ECO MT (hail totaled 5/8/17 103,600 miles @42.5 MPG)
2010 Mit Lancer GT MT (traded for ECO @31K miles)
2002 Pont Montana AWD - title to son at college graduation
1990 Pont Transport (traded for Montana @240K miles)
1986 Fiero GT MT (traded for Transport - needed more seats)
1985 Fiero 2M4 MT (traded for Fiero GT @8K miles)