The batteries should weigh roughly the same as everything else on the airframe combined.

With a given aircraft -- everything known except for the mass of the batteries -- the absolute maximum flight time occurs when the weight of the batteries is twice as much as the weight of everything else on the airframe combined. However, many other characteristics -- time to get up to altitude, responsiveness, avoiding stall, etc. -- work better with less battery weight, so a better rule of thumb is batteries roughly the same (one times) the weight of everything else combined. Reference: Andres 2011. Optimal Battery Capacity. via Heino R. Pull.

This rule of thumb applies to all kinds of battery-powered aircraft -- fixed-wing, quadcopters, helicopters etc.

(Forgive me for recycling my answer to Effectiveness of a Mobile Robot In Relation To Mass ).

EDIT: fixed a self-contradictory sentence -- thanks, Gustav.

The batteries should weigh roughly the same as everything else on the airframe combined.

With a given aircraft -- everything known except for the mass of the batteries -- the absolute maximum flight time occurs when the weight of the batteries is twice as much as the weight of everything else on the airframe combined. However, many other characteristics -- time to get up to altitude, responsiveness, avoiding stall, etc. -- work better with less battery weight, so a better rule of thumb is batteries roughly the same (one times) the weight of everything else combined. Reference: Andres 2011. Optimal Battery Capacity. via Heino R. Pull.

This rule of thumb applies to all kinds of battery-powered aircraft -- fixed-wing, quadcopters, helicopters etc.

(Forgive me for recycling my answer to Effectiveness of a Mobile Robot In Relation To Mass ).

EDIT: fixed a self-contradictory sentence -- thanks, Gustav.

The batteries should weigh roughly the same as everything else on the airframe combined.

With a given aircraft -- everything known except for the mass of the batteries -- the absolute maximum flight time occurs when the weight of the batteries is twice as much as the weight of everything else on the airframe combined. Reference: Andres 2011. Optimal Battery Capacity. via Heino R. Pull.

This rule of thumb applies to all kinds of battery-powered aircraft -- fixed-wing, quadcopters, helicopters etc.

(Forgive me for recycling my answer to Effectiveness of a Mobile Robot In Relation To Mass ).

The batteries should weigh roughly the same as everything else on the airframe combined.

With a given aircraft -- everything known except for the mass of the batteries -- the absolute maximum flight time occurs when the weight of the batteries is twice as much as the weight of everything else on the airframe combined. However, many other characteristics -- time to get up to altitude, responsiveness, avoiding stall, etc. -- work better with less battery weight, so a better rule of thumb is batteries roughly the same (one times) the weight of everything else combined. Reference: Andres 2011. Optimal Battery Capacity. via Heino R. Pull.

This rule of thumb applies to all kinds of battery-powered aircraft -- fixed-wing, quadcopters, helicopters etc.

(Forgive me for recycling my answer to Effectiveness of a Mobile Robot In Relation To Mass ).

EDIT: fixed a self-contradictory sentence -- thanks, Gustav.