How to open the game menu (where you use items, etc) during a battle?

I've done it before but it just wont open. Do I need to use a specific script(s)?

um ... why do you need to do this via script?  There is an action to open the Items menu on each actor's turn in battle.

You can open the Item menu from the game map with something like this:

SceneManager.call(Scene_Items)
but I don't think that works in battles, because the item window in battle isn't handled by a separate scene.  Are you SURE you've done it via a script call in battle and not just on the map?

No, I mean, THIS menu: 



Inside a battle, like this: 

That menu in scene can be called with this SceneManager.call(Scene_Menu), that's the usual way to call it. You need to add a custom command in actor command window or party command window in battle. 

Thanks.