About the battery kits for the APM Plane:
Is it possible to install more than one battery (parallel connection) inside the plane fuselage in order to improve the mission autonomy.
What is the autonomy of 1 battery fully charged for the APM Plane?
Yes, you can parallel two LiPo batteries in your plane to get extended flying times.
If you use two batteries your flying time will not double as you have to account for the extra weight of the second battery which will reduce lift at any give air speed and cause the motor to use more current.
Do you have an idea of the autonomy in hours-minutes of a APM Plane complete with telemetry, Video OSD/FPV and one battery fully charged ?
That would be very hard to pin a figure on, I am sure though you could see at least 20 minutes of flight time.
Depends on AUW, drag, level or climbing flight, wind, etc, etc. There is no definitive answer with the info you provided. I believe the APM Plane is a Bixler/EZ Star type of plane. As such, you can get a 2650 mAh battery for flight and a 370 mAh battery for video and fly for 30 minutes at 80% battery under the right conditions.