The Chevy Volt is not a series hybrid. It can operate like one, in some modes, but GM actually found, especially for Gen 2, that a mixture of series and parallel is most efficient.

When the Volt runs out of battery, it's almost not noticeable apart from engine noise. The performance characteristics in hybrid mode are almost identical to EV mode in terms of torque/acceleration.

It's an engineering marvel. I love mine. Shame GM killed it.