The radios in my shack are now powered by a 12V flooded deep cycle lead acid battery with 105Ah capacity charged from a 100W solar panel. So far all seems well. I'd like to know how low the voltage drops in the early morning so my project is a voltage monitor that can be logged to disk.
An ESP32 board with Wifi and an OLED screen was used. The analog input has a resolution of 12 bits. I grabbed bits of sample code from the ESP32 Arduino examples and created a tiny web server that registers itself on the network using multicast DNS so that a web browser can simply poll the ADC value.
The maximum that the analog input can take is 3.3V so I used a resistor divider with 5k and 1k to divide down up to 15V to something the input can handle.
A 7805 regulator was used to give 5V to power the board. All seemed well.
Unfortunately the Wifi is not strong in the shack and the ESP32, while it could see the network on a scan, could not connect.
As you can see from the photo above, I tried cutting the on-board antenna and attaching a wire antenna. I'm not sure that this improved things but in any case it didn't fix my problem.
Of course doing all this over Wifi with a web server is a rather complex arrangement so I have another, simpler plan under way. I'll post when it's been running long enough to draw a graph.