MOSFET N-CHANNEL don't switch
SOLUTION: If you are "cutting" the ground make sure you are measuring your output from where you realy want to measure it !In my case I was measuring Vout from Vout of the LDO and the negative pole of the battery, so when Vin>2.5V Vout=2.5V, but when Vin&lt;2.5V the MOSFET disconnect the ground of the battery from the rest of the circuit so between Vout and the negative pole of the battery there is a remaining voltage. But if you are measuring between the 2 pins of J1 or J2 you should see 0V, but if you are measuring from Vout on J1 or J2 and the negative pole of the battery you are not measuring what you are expecting... So this is why I got strange voltage on my multi-meter...In short:When you are measuring a voltage with your multi-meter make sure to measure with the good ground reference !