the thing i notice with a fresh battery is there`s so much power to get it in the air and it`s so responsive.
it only takes a tiny movement on the sticks to change altitude/direction.
as the battery starts to drain the responses don`t seem to be as quick so it means slightly,just slightly,bigger stick movements.
this maybe why you think it`s more stable with a battery that`s losing power because as you`re still learning your stick movements will be slightly exaggerated
keep practicing and it`ll all fall into place,for the first few months i thought it would be IMPOSSIBLE for me to hover nose-in but now it`s as easy as tail-in