Thanks for your answers.

The batteries i´ve tried were both old and one of them were the drowned one. The other gave pretty poor power before the boat sunk and i couldnt use it with a 17 turn motor. But now i´m just trying the stock motor to see if i can get it to work.
So the batteries can be bad.

I have used them sometimes over these two years to start my T-MAXX and i tried the equipment one time last year in a car but with the same result.

The engine does not cut when there is no load on it and sometimes i can drive full throttle for a sec or two.

I hope It´s the battery cause i´m on my way bying an 8,4 to it anyway. It´s just that i dont wont to spend money on it if it doesn´t help.