So a couple things about the fusion cores and the way power armor works really annoys me in this game.
They have a survival mode where you can't insta-heal yourself by eating 3 tons of raw roach meat while your enemy stands by and watches, and yet the moment your armor runs out of power, the old fusion core ceases to exist and a brand new one suddenly appears in it's place out of your pocket.
I think there should be a the option to make fusion cores just run out and have the old ones be ejected when they deplete and force you to get out of your armor and put a fresh one in.
Could make it so the old cores get shot out the back before they overload and disappear in a puff of smoke or explosion, forcing you to finish whatever fight you're in bogged down by the weight before you have a quiet moment to put a new core in.
It also annoys me that when you use an empty suit of armor without a core in it it automatically takes a brand new core instead of asking you which one you want to put in, but you have the option to do that yourself by opening the inventory so I can live with that.
Also that nearly empty cores are just as valuable as full ones although they cannot be recharged and disappear when used up makes no sense. It always makes me nervously watch the last 10% so I can switch it out with a fresh one before it disappears so I can sell all the depleted cores.