Aguyfromohio wrote:Many years ago I was part of an engineering team for the main battery on the F-16.
We could only accurately know the state of charge of the battery by having a little micro processor measure the current entering and leaving the battery, and keeping a running tally of amp-hours remaining. We had a PhD electrochemist on the team, he assured us there is nothing you can measure at the battery terminals that tells you much. The more expensive battery monitors like those mentioned above measure current and perform that kind of amp-hour accounting. Our system had a lot of fancy correction factors for temperature, and rate-of-discharge, and cycle life history to improve accuracy.
Of course it may be worth asking the question “why try at all?”
If you are off grid and not able to charge, just use as little power as possible and when the battery is depleted that’s that. If you have a high quality smart charger wired in to the shore power circuit, plug in whenever you can and the battery will stay as charged as possible.
The Air Force cared because they had jet fighters not ready to go due to dead batteries that were being depleted by ground crews and failing early due to abuse. Our system disconnected the main battery at certain points when the ground crews ran the batteriy down by talking sports on the giant military radio or were goofing around too much raising the canopy up and down. They had to go outside to push a RESET button, and our memory data would tell their superior officers who was ruining the batteries and reducing the unit readiness. The average camping trip is less critical.
This is a less fancy, less expensive version I use
bayite DC 6.5-100V 0-100A LCD Display Digital Current Voltage Power Energy Meter Multimeter Ammeter Voltmeter with 100A Current Shunt
https://www.amazon.com/dp/B013PKYILS/re ... KAb6P71JNNI have it on a dpdt switch. When discharging it records watt hours used. Then when charging, I flip the switch, reset the guage and it tracks watt hours sent to the battery. It’s not perfect, but easy to see when I’m drawing more than I can afford.