A couple of years ago I tried using several different nav apps and ended up getting a lightly-used 12.9" iPad Pro from a seller on craigslist. I usually use AquaMaps but also use Navionics. Both are great programs. I really like having the big screen.
I prefer to run from the flybridge but in rain or other adverse conditions I will run from the pilothouse. I like being able to carry the iPad back and forth.
I installed 12-volt USB outlets at each nav station over five years ago, and the iPad Pro will slowly drain down over a 4-6 hour stretch. This summer I will replace the ports with higher-output versions.
My advice, FWIW, is get the biggest screen size you can. Put on a screen protector. Get 12-volt USB power wherever you're going to use the device.
Finally, I made a mount on the flybridge to securely hold my iPad. I don't want it flying around when we hit the occasional wake or rough water!