Take some nighttime cold medicine and go night night.
Look outside
make small talk with strangers
get bad diarrhea and be stuck in the BR
Bring non electronic games like cards
bring a piece of wood then paint it and watch it dry. add more coats for more fun!
Bring a encyclopedia to read
check the pockets and corners of the seats and see what you can find
Learn a new craft
Tell people that you have a contagious disease that cant be cured then fake a sneeze on them
Start a sing along and get everyone to join in
Its funny when we have lots of options to stay relaxed but we can't maybe because we tired to do nothing but to sit all day long. And I suggest that you avoid reading while on a travel the reason is we just feel irretated because we cannot focus on what we read on and boredom may attack any second.
Best thing to do is to listen in music but since you just said that your battery doesn't last I suggest that once you play music make sure that it is relaxing like Leaving on a Jet Plane it is so popular but cool, you have one more option if your battery is out of charged try to closed your eyes and play music with your minds and you never know that you may fall asleep :) it is effective I always do it while I'm on long travels.
It is possible to get phone chargers that are powered by batteries. You could also do a "find-the-thing" type of game, where you make a list of things you might see while on the ride and cross them out when you see one.
You should just try to find some people you don't know and talk to them and get to know them better then you ever have. This would pass time as they may be interesting and you could learn from them and teach them things.
Be sure you are tired no sleep for a while, then taken a long nap is great