This is looking really good!
So I took a close look at the schematic, and there's an issue with the voltage divider that's troubling me, and I'd like to get your opinion on it.
So in the first schematic you released (with no voltage monitor), the current monitor was electrically isolated from the battery buss. The current sensor gets its power from P3, presumably good, clean power.
Now, with the voltage divider, the voltage has to be referenced against something, so the P3 ground is, by necessity, tied to the battery buss ground.
Are we setting ourselves up for some kind of ground loop issue here? Perhaps with stray currents flowing through the ground wire of the P3 wiring harness?
I still like the idea of having a voltage divider that measures true battery voltage. But I'm wondering if it would be forward-thinking to isolate the P3 ground from the battery-buss ground with a 0-ohm resistor, so that if there is some sort of ground loop issue, we can cut that lead, or install a ferrite bead, or what have you.
I'm trying to think of an easy way to keep the two grounds separate, but still measure battery voltage. Short of bringing two voltage pins back to the A/D for differential measurement, I haven't come up with anything good.