Hi Gilad
Hope you can view these inclosed PDFs
As you can see the set up gives
.a short flying time for 3D etc and a bit longer for mixed relaxed flying
You seem to have a prop that is a bit to big. you get a good thrust with a smaller 10x4.7 prop
in both cases not full efficacy
from the set up. Yet the short flying time calculation may point to power drain that is a bit to high
It is 16.6 Amps for the 11x4.7 and 10 Amps for the 10x4.7 prop
In both cases you have more than 120W / Lb with the 11x4.7 it is 150W/ Lb
There is a power drain during max use
So your battery problem can be from all these factors together, including miss usage and Storage
The Stall thrust is: 721 Grams for the 10x4.7 and 915 Grams for the 11x4.7
Ronny