I've never noticed mine losing miles in Hold mode. Whenever I use Hold, it will run the engine at a high idle when I'm coasting or close-to-coasting and the battery power gauge on the left goes down into the green while it returns to the setpoint. This only occurs after heavy acceleration. I've driven over a hundred miles in one Hold trip before and never lost a single mile of EV range.My early impression--subject to revision--is that my Gen 2 does a worse job "holding" EV miles than my Gen 1 using it on the same commute.
I can't figure out if Gen 2 tries to "get back" to the held SOC setpoint, especially if it requires battery power beyond the ICE alone. On my Gen 1, the ICE (mostly) added charge to maintain the HOLD setpoint--but it also operated in a serial hybrid capacity. On my Gen 2, it seems that whenever it needs battery + ICE (like hard acceleration), it doesn't try to "replace" it. Maybe a characteristic of the parallel hybrid setup? Or maybe it tolerates more deviation?
It seems this member also noticed this issue on a 2000-mile trip where he used "hold" the whole time and lost half his EV miles. http://gm-volt.com/forum/showthread.php?284690-Questions-about-Hold-mode
What's going on here? Is the battery just augmenting the ICE in Hold mode? Do I need to drive within the (lower) power demands of the ICE alone in hold to avoid drain? Under what conditions (if any) will Gen 2 maintain the Hold setpoint?
Now, if you're driving up a steep slope such as a mountain the whole time, it's not going to have time to recover the lost mileage unless you drive flat or downhill for a while in the same trip afterwards. Note that the setpoint gets reset to the current SOC any time the vehicle enters Hold mode.