Screen brightness is a battery hog. I like mine bright, and it will eat up a full charge in no time. 50% brightness barely touches the battery.
Last week DFW-IAH I used 75% of my battery, from preflight to taxi in. Daytime flight, max brightness, screen on the whole time. OTOH, I've had 50% left after LAS-EWR. Night flight, lowered screen brightness, screen off after climb out until briefing.

Get an OEM Apple 3 meter cord. It will reach from the FO's outlet to your ipad tray. I have a 2 meter cord, which is long enough to charge if you hold the ipad in your lap.