I designed this vehicle battery monitor a little while back using an ESP32C3 running ESPHome and a wide input range switching power-supply with very low quiescent current to keep track of my vehicles' batteries. I have an old tractor, military truck, and vintage car which all see little use during winter months. It works with 12V and 24V systems, and has been really great for helping me avoid dead lead-acid batteries, which are expensive to replace.

Specs, ESPHome config files, and more info are here: https://granzscientific.com/product/bm1/

Also here: https://www.tindie.com/products/granzscientific/wifi-iot-vehicle-battery-monitor-esphome-ha/

Would love some feedback from the community!