Had the same problem with mine...and it turned out to be a dead cell or 2 in the battery... Replaced the battery and all good.
Check the voltage on ur batt. should be a little over 12volts...then turn on the lights if the voltage drops off then its prob the battery(or could just be dead...so charge it up then try again) if same(dropoff) then batt is bad...
If u do this while the quad is running the batt should be over 12 volts and when you turn on the lights if it is still over 12 volts its not the stator(it is continuing to charge the batt)... and if u turn the quad off with the lights on then the voltage drops on the batt...the batt is prob bad.
Good Luck!