i just got me a second hand dji phantom.
I have some problems with battery life.
i got 3 batteries with the drone, but hey where all lasting 1-3 minutes max before red light and autoland sets in.
i went out and got a 4th. battery, and a new charger for it. but it is still the same.
i have messuret all the cells to be 4,2v and the battery has 12,6v on all the batteries.
I am starting to think there is something wrong with the drone it self.
could this be a firmware problem, or is it morelikely that the drone it self is broken?

it flyes really great, and the motors seems to be spinning ok, the two of them seems to be a bit harder in the magnets, but not much.

i really hope one of you will be able to help me. thanks

I have now set the  the loss in voltage to 0.7.
and i got allmost 10 minutes.
what is the minimum voltage when this gets dangerus?
how far down can the phantom one go ? 10,5 v or?

What is the voltage after you land.  
How many mAh are you putting back in when you recharge.
You want about 80% of the batteries capacity to be left in the battery to prevent damage tot he battery and give you time to land when the warning lights come on.
The voltage drop value is not meant to be the main value for adjusting the warning level.  It is the value which reflects how much the battery voltage drops due to load on the battery in flight.  You adjust it so that the actual battery voltage after you land when the warning lights come on is equal to voltage set in the assistant.