This game is really satisfying, I spent much longer than expected playing it! I love the pixel art car, and the light and shadows with the day/night cycle is really well done. I spent so long playing the game in fact that I found a bug. If you upgrade the energy efficiency of your weapon enough, at night time when you shoot you gain battery and can gain above the max amount. The charge above the cap instantly goes away when the day starts and you can only gain the extra at night.
My one piece of advice would be to increase the sound variety for the gunshots and zombies dying. When a common action is going to be repeated often, I try to have 2 or 3 different variations of the effect play at random. However even if you only have one a nice trick to increase variety is to slightly modify the pitch by a random amount, most tools will let you do this! I like to start at .95 - 1.05 of the pitch and see how that feels for the particular effect and adjust from there. The slight variation helps the player not notice it's the same one or few sounds over and over again and makes the game feel a lot better even if they don't notice it consciously.
Excellent job!