I triggered the ICE for the first time with acceleration. I was surprised that the engine remained on until I turned off the car a short while later. Plenty of battery left - about 50%. I was in normal mode. Is this expected behavior. If so, why?
Yes, expected behavior. Why? "Because that's the way the engineers designed it." I suspect that one factor is that once the engine starts they want to let it get warmed up completely before shutting it down. But anything we speculate is . . . speculation.
I've definitely noticed the ICE running longer after a burst of acceleration now that the temps are low. Smart engineering IMHO.
Burning hydrocarbons (like gasoline) generates a LOT of moisture; while the exhaust system is cold that will condense and potentially damage the exhaust system, whereas warming the engine will convert the water that's condensed back to water vapor, and the exhaust system will have a chance to dry out again.
A major issue with hybrids in general is the engine doesn't get hot enough, leading to oil sludge. Honda works around this by saying if the engine starts, it has to get fully warmed up before turning off. If it starts a second time it should turn off quicker. Basically, if you start the engine it will be on for 5 or 10 minutes. Maybe less in hot weather, more in cold weather. Use Econ mode if you want to avoid accidental engine starts (it will still start in certain situations).
Thanks for the information. That makes sense. Since my drive was not very long, the ICE did not stop until I shut off the car. I assume from the responses that the engine will eventually stop in a longer ride.
Yup, it'll eventually turn off. It's a tad frustrating when you didn't mean for the engine to turn on and you can feel the money leaving your pocket as the gas burns but you get used to it. Drive in econ mode, it takes quite a bit to get the engine to turn on in that mode.