Followup to followup on my Prius battery

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I jumped the car to get it started and let it run unattended for about eight hours (I left it parked in front of my house, but I have Zoom cams in front, so the likelihood of theft was low), and then turned it off.

I am curios, if you leave a Hybrid car running, does it actually run the gas engine or just idle on the lithium battery? I know my Volt would not run the gas engine, unless I opened the hood.