I figured out what’s happening: when you launch the game there’s no sound at all, but if you go into the settings, you can see that both the Master and Music sliders are set to 40. To actually hear something, you have to either raise Music to 100 or tweak both sliders to above around 70.
This seems like a configuration issue with Unity’s audio system... I would need to see the configuration to explain it better or to understand more clearly what’s going on.
About the batteries, I see what you mean… hmm… maybe make the light flash? Adding a sound could help too. Other options might be a slight vibration, a small outline or tiny particle effects that appear only when the player is nearby... anything that helps spot them up close without making them too obvious from afar.
I hope I explained myself well (English is not my first language).
I 'm going to change my previous comment and the rating to be fairer, sorry for the inconvenience.