Interchange F450 Battery between 3S and 4S

Hi,

Currently, I am using a 3S battery with my F450 pixhawk quadcopter running with ardupilot 3.4. The problem I have is the flight time is very less around 5-7 mins. So I am going to buy another 4S battery to extend the flight time. I want to know, if I change the battery from 3S to 4S, will it affect quadcopter dynamics. (tuned PID, alt hold, loiter mode, stability, etc). Will it be safe to use 3S and 4S batteries time to time. I’m going to use 3S battery until its voltage is low and then the 4S battery. Then again 3S once I charged it. Please help.

Thanks

The copter is going to fly very differently from 3S to 4S.
The main reason is you are increasing the rpm of the motors for any given throttle value.

So if you have it tuned well on 3S then 4S it will be very twitchy, even uncontrollable, depending on your craft and it power.

You would be better served by just increasing the capacity of your 3S, or running 2 in parallel.
Or going all 4S.

Thanks. Even switching between same capacity batteries with different weights affect the flight characteristics and make my quadcopter unstable.