The basic problem with really long range Quad operation is simply energy density. The amount of energy able to be carried is still very limited. If you had a nuclear powered Quad then the range would be virtually unlimited.
The real problem is the energy burn and the simple fact that the entire lift of the craft, (providing an equal and opposing force to gravity), is sourced directly from the total system energy. This constant energy burn places a definite time limit on the crafts ability to remain airborne. To stretch the range of a Quad it MUST travel at a fairly high speed such that the energy used for forward flight is large compared to the static energy burn. In other words to burn as much energy going forward as is possible before the lift drain uses the entire energy pool.
Due to blade drag and the requirement to burn energy to remain flying all rotorcraft are destined to be relatively short range unless they are large enough to carry a large energy store. A simple method to reduce the energy burn required to remain aloft is to add an aerodynamic lifting structure, (a wing), but this on a Quad alters it away from its original design.
When you add a larger battery the weight is increased and so is the energy required to keep flying. As for swapping batteries with other airborne craft it would be interesting as the overhead position of the rotors and the central under location of the battery would make swapping out a battery an extremely interesting problem especially when most radio systems would shut down without battery and so would the drive motors being used for lift.
A static "Squat and charge" via an umbilical cable could be used but the charge rate would need to be so high that it might either take an extremely long time to charge the flight battery whilst in the hover or there would be a severe risk of a battery failure, (Explosion or fire), due to the fast charging of a hot flight battery.
The things that you need to solve for long range flight is to increase the energy store without weight penalty, decrease the weight without reducing the energy store size, reduce the rotor drag and thereby reduce drag induced losses, fly the craft at maximum forward speed possible, or provide a device to increase the lift not directly related to the energy burn. (adding a wing or a dirigible type ballonette may remove its classification as being a Quad though).
Just my thoughts!
Have fun!