I tried dragging food and batteries from my inventory to action bar and I can't. How come I can't put a battery in my action bar, or food item, or weapon? Bug? Kind of annnoying.
Hit I for inventory and then K. From there, if you choose Status, and click on your ship, you can drag batteries and stuff into your ship's devices squares, and then they should show up in P and/or they will already show in your space tray bars for use any time you want them.
I don't know why they are coded that way - I guess it must have something to do with Cryptic's game engine. Most games allow you to drag from inventory straight to tray bar slots if the items are usable in game. However, I have seen some other games code some things differently as Cryptic has done here, so who knows why.