Pretty often you still need it. In recent experience almost all virgin flights and about 50% of BA flights still need them.
I tend to just load up a tablet with stuff I want to watch though. Unless you're on a new plane or recently refurbished the screens are crap quality anyway.
I did exactly this with my last trip back to HK, little did I know I was flying on a Boing 777 with pretty amazig movies and even USB ports... I was like... oops... must pretend I am not excited and keep a deadpan face on...
Yep, lithium ion battery pack.
Do you need a plane adapter still these days?