Hi! Good job on the game! I've seen a few videos about it and many people seem to have trouble to remember there's an inventory. I would suggest a very simple tutorial. You give the player the flashlight right at the beginning but without batteries and force him to open the inventory ("Press TAB to open the inventory" and "Click on the flashlight to use it") but as they don't have batteries you can display a message saying something like "I need batteries to use it." so now the player nows how to use the flashlight and you can still put the batteries in the drawers. You don't lose any gameplay mechanics.
Honestly, I don’t think a mechanic like this would help in a game that relies on speed to win. In order to secure all the windows, you have to really scramble for the flashlight and the basement to get the boards. Adding a mechanic where there are text prompts and additional steps (i.e. finding the batteries, getting a prompt to enter the inventory, add the batteries to the flashlight, etc.) *every time* you have to start over would likely cause more problems than it solves, and make the gameplay tedious.
That said, hotkey assignment is useful when an inventory isn’t intuitive or vital. So it may be more useful to simply present hot key reminders (like space bar for turning the flashlight both on and off) in future titles.