multiwii Quadcopter drift after sometimes of stable fly

[KingAbdel]

hi guys, i have a problem with my homemade quadcopter, actually, the drone works very well for a while but, becomes instable after maximum 3 minutes of flight. i want to clarify that when setting the PID in acro mode, when i put the throttle to full the PID works very well and drone response well for at least 2 minutes and after i drastically lose the throttle and it is at this moment that my drone becomes unstable (it pitches and rolls negatively) and i lose all control over the throttle, from then on i have to disarm then rearm need help please, i am a beginner

[Hamburger]

battery weak after those 2 minutes?