There are many good questions here I had to research and all answers are available in the link provided
Starting on page 11 it speaks of the different modes and as you read on explains in laymen's terms how and when to use the different ones.
While you can have a preference and use whichever one you like, reading and heading the instructions will give you the best economy for the driving conditions present for each driver.
Understanding how a PHEV is different from the previous hybrids will help a lot in knowing which mode (EV, HV, HV/Charge, Sport) is best.
In short, this will work for most of us. If driving in municipalities where speeds are less than highway speeds and trip distance (round trip) will be less than 20 miles than EV is the most economical. If your distance is longer and/or highway speeds are involved than starting out in HV will run the ICE (internal combustion engine) enough to 'maintain' a high charge on the batteries. If you are traveling cross country for a few hundred miles, than when the battery condition falls below 50% if you select HV/Charge, the battery will come back up to slightly over 50% if you drive far enough. On a cross country long drive your MPG will probably be in the mid-low 40's unless you drive over 70mph. If so, you'll get there slightly faster but it will use more gas.
Everyone has different driving conditions so a better understanding of the way the system is designed to work will offer the best economy for everyone. With the differences in routes, distance, and speeds, we will all get a different set of numbers but can operate the car to get best under each set of conditions.
I've owned three Lexus hybrids prior to the Clarity. I have 3800 miles now and think this is the best design for the money currently available.
I really don't understand the question. The car does not start the way a conventional car does. The car has two types of batteries. One is the high voltage battery that propels the car and the other is a 12 volt battery that cars have been using for 100 years (in the 1950s they switched from 6 volt to 12 volt). They only thing the 12 volt battery does is boot up the Clarity's computer. Once the cars computer boots up the high voltage battery (Chevy called it the traction battery) propels the car and also keeps the 12 battery charged. The only way the car will not start (it is more accurate to call it boot up) would happen if the 12 volt battery to boot up the cars computer, and the only way that you can drain the 12 volt battery is to let it sit in your driveway for a few months or it can also happen if you leave the headlights on and forget to turn off the car.
This is just my opinion based 3 years of owning a volt and driving close to 2,000 miles on my Clarity. I have driven the car for almost 2,000 and I haven't used more than a few drops of gas.
I would like to hear a reason for not leaving it in EV all the time other than the manual said so. If you leave it in EV the computer will run the car occasional to keep the ICE lubricated. The car is so quiet the ICE could be running and you will not know it . I noticed that the gas gage had not moved since I got the car so I pulled into a gas station to verify that the fuel gage was working. I filled up and all I could squeeze in was 0.04 gallons of gas which too me meant the the Ice was burning off a few ounces of gas occasionally.
I asked this in another thread I started with out many responses. I asked why people bought and electric hybrid. My goal was to bur as little gas as possible. so far it seems to be working which I verified by trying to add gas at about 1,500 or 1,700 miles and only being able to fit 0.04 gallons.
If most of your trips are less than 55~60 (I normally get 58 to 62 miles on a charge) You should be able to drive 6. to 12 month before you add gas.
So I would really like to learn the reason why anyone would use any gas when they could go for months without needing gas...
By the way the Volt is programed to burn off off a tank of gas if you haven't used gas in a year. The Volt tank is pressurized to keep the fuel fresh but after a year you probably are going to want to burn it off by driving the car and adding fresh gas.