Hi Bob one thing to remember is that if you have not selected EV only mode on ( EV button by the gear stick) then at 24mph it automatically starts the ICE( or if the heater is on , as it needs the heat from the ICE to work , like a normal ICE car)
If you do a long journey in ICE then when you are coasting / going down hill it will charge the battery a little ( I did 150 ish miles to the lake District on the motorway and it charged the battery for about 8 miles range in EV mode only.
Really you do not want the ICE to charge the battery as that is expensive and inefficient, it's better charging it via electric ( granny charger / EV charger).
There is a setting that allows you to charge the battery via the ICE but the mpg from the ICE will be affected badly( I got 40 mpg ) I think someone found in the early days of this forum.
So basically charge the battery via home electric, then it's up to you to either let the car do it's turning on the ICE at 25 mph, or manually press the EV button, and you will be locked in EV mode .
I hope that helps