Hey I played your game! I love the minimalist aesthetic, and the game mechanics are interesting. I even kind of like the way you can store batteries based on looking at your belt. But a lot of it felt very unintuitive, and I was stuck on the tutorial for a long time (I never actually figured out how to put the battery into my shield and only knew that after skipping the tutorial). Also, after putting the first battery in the door, it's not clear that I have to grab it again to recharge it. I did figure that out, but then I didn't realize you had to wait for charging, so I put an uncharged battery in the door and it seemed like I couldn't get it back out, so I had to restart. So I think the tutorial could use a lot of work. Maybe you could start with forcing the player to charge a battery so you know how that works. Also, I'm not sure how to make it clear how to put the battery in your shield, but demonstrating that should be clearer too. Then by the time I tried the level after the tutorial, I just kept dying from the enemies before I could get out of the first section. So I was never really able to progress past that. I don't know if it's just a me problem, but I feel like the onboarding and early game needs to be restructured to ease the player in.
I guess my main takeaway is, since you have such a novel set of mechanics (which are really cool!) you really need to hold the player's hand and make each part of it very clear. You have a cool base here, so just a lot of iteration and testing and should be able make something great.