So, I once tested 5 weeks. Conclusion: making with an unmodified DJ Phantom I sense.

With the standard DJ Phantom I is a longer flight time is also possible. But if you have - like me - accessories on Copter (Cam, Gimbal system) weighs the copter too much. Specifically with me too much 253g of weight. The Copter alone weighs 810g with a standard battery and without external devices. The max. Payload is loud DJ I 350g. Altogether 1160g.

With two batteries, Cam, Gimbal weighs my 1413g. The flight time with a battery is 7.40min with me. Flight time with two batteries = approx 10 to max. In 11 minutes. This result is due to the high weight with two batteries.

Solution: Install stronger & better engines and use 100% balanced propellers made of carbon. Thus one gets a little more to flight time.

Summary: Quite Copter well, with additional equipment such as Cam, Gimbal, etc. only through better engines and propellers sense.