I really do enjoy the style that you've gone for here. I recognise the map pack (shout out to Comp-3) but aside from that some feedback that I have is that it is really strange that to combine batteries into the Flashlight you have to click on 'Use' on the battery instead of 'Combine', which is surely what that option would be reserved for?
There are also some typing issues (but it seems English might not be your native language and this is only a Demo), but one other thing I would add is that the battery goes down very fast. Not that the player could run out in the demo, but it ticks down 1% a second, so if this was a more fleshed out game you'd need to have batteries literally everywhere to stop the player getting stuck without a light, so you might want to slow that down if you develop this further.
I hope you do! I did really enjoy the short taster that this demo has!