I'm not sure if anybody already did this but I've made a script for accessing equip screen in battles and thought I'd share it here in case anybody would be interested. It basically just tweaks of Scene_Battle and Spriteset_Battle classes. I'm including complete scripts in attached files so in case you're not interested in scripting, just open these files and copy their content to their respective pages in script editor. Just be careful, as it'll rewrite any other scripts you may have had there. I strongly recommend backuping them first in case anything goes wrong but I've tested them on vanilla scripts and it works fine.
In case you'd be wondering what changes I made I'll try to explain step by step so you can make further tweaks wherever you need.
So first let's look on Scene_Battle 1:
First I made another line on command window with the text "Equip" and added an corresponding attribute on @actor_command_window. I've also appropriately raised its position to @actor_command_window.y = 128, so it would fit battle screen with the new command. Then I've created variables for disposing of equip windows, as a condition I've left just if @right_window != nil. There are 7 equip windows in total but all are being created and disposed at the same time so I left just 1 window as condition. That's pretty much it for init phase.
Scene_Battle 2 deals with pre and post battle phases so there's not need to change anything there. Most changes were in Scene_Battle 3:
Most of the things here is basically just Scene_Equip class split into multiple parts so it would adhere to Scene_Battle 3 structure. First thing that needed to be updated is update_phase3 method, so I've created another condition here for updating equip window: