The MM in the Gen 2 Volt isn't as good as the Gen 1 Volt. In the Gen 2, MM maintains the battery at 14% charge (as displayed by the MyChevrolet and RemoteLink apps). This works out to about a 2 kWh reserve. While two green bars show, after turning the car back to Normal Mode the second bar almost immediately disappears, and you get maybe 7-8 miles of electric range.With our 2016 Volt we use hold mode more so than mountain mode. If we plan on going to Portland Oregon for the day I just drive on electric and than at 20 miles or so switch to hold mode. Once in the city area we can switch to normal, electric mode for all of our city driving.
From what I have read here, the Gen 1 MM reserve is more like 40%, or about 4 kWh. (Is 40% what MyChevrolet/RemoteLink apps show? Or just a guess because 4 bars of 10 are displayed? Be nice if a Gen 1 owner could confirm.)
For its intended purpose, climbing mountains, the revised Gen 2 setting may be fine though. This because the Gen 2 has a more powerful ICE than Gen 1 had, and perhaps because of the improvements in the transaxle design allow better efficiency as well.