[darkmighty]

If you battery is dead and your engine isn't running, isn't the battery the priority anyway? Having backup batteries to provide initial excitation for generators should not be difficult. They just need to start it, afterwards you can use the output for self-excitation. Worst case, you'd just use a tiny PM generator to bootstrap the process.

I think there are other more significant trade-offs between induction and PM motors. Induction motors/generators are significantly heavier, and have significantly lower torque (i.e. can extract less lower at low speeds when used as generator). Their main attractiveness comes from lower cost, reliability, and decent efficiency at high speeds.