...and history, is important to know when was invented the wall socket.
You are missing the point, if they have knew how to make electricity(physics) they could get back to the present.
Breaking Bad's battery scene is really good example:
It also good knowing when appear first potato or lemon on earth.
You don't need sofisticated chemical battery if you have enough potatoes. XD
(i say this just for lolz.)
It's not work like this, you still need to know physics and math. And there are many kinds of energy resources.
Well, i suppose you're right, also a hamsterweel dynamo will work, but it require too much time for build it and tame dinosaurs, also coal still work, but is better don't do it during time travel, it can create an undesidered steam-punk time line.
