48V Generator-Battery Charging Circuit

I am building a vehicle system having an I.C. engine powering a 48VDC generator, which charges a 48V battery, and also serves power to a 48V vehicle drive system. The engine/generator will be started when the voltage (battery-sensed) falls to 40 volts, stays on till voltage reaches 48V. Questions: During startup, as the generator spins up, its output voltage would be increasing, yet its output is connected to the battery. Is this an issue, should the generator then be isolated from the battery circuit until it achieves the required rpm?