In uk.d-i-y Martin Brown wrote:
I wonder how it damages the vehicle more than running out of petrol in a
normal vehicle and running crud from the bottom of the tank through.
Anyone have an explanation ?

As I mentioned elsewhere in this thread, the car is designed with petrol and
electric systems as complements of each other. This enables each system to
be optimised for the functions it's best at, rather than having to cover
every eventuality as a single-mode car would be.

If you run the car with only one system operational, that system is run out
of its usual operating range, which can cause undue stress. In a hybrid the
petrol engine is the ultimate source of energy and the fallback system in
case of problems. Running without it means the car has no option but to run
the electric system out of tolerance if you make excessive demands on it
(the car not being able to tell whether not responding might cause danger to
the occupants; it is safe to not start but it is not safe to shut down
without warning).

Theo