Nope it’s a separate battery used like in a normal car to power the low voltage stuff so you don’t have to use high grade power lines to run the windows and doors
During the pandemic my car sat in the garage until the battery died. After 7 hours of charging it, turned on the car and found the hybrid battery was almost full.
I get why the high and low voltage systems are separate, but damn that was one of those “Really!?” moments…
It’s much much much cheaper to use the same 12V systems that other cars use.
Kia/hyundai solved this by having a disconnect on their (li-ion) 12V battery. When the voltage gets low it completely isolates the battery. There is a button inside the car that reconnects it right before starting the car.