Calculating AH usage Based on SOC

Gjac wrote:

DanNJanice wrote:
Yes, your method would work. It would not be real accurate, unless you can accurately measure SOC. That is a problem, as the meter needs to be accurate, and the batteries need to be at rest for several hours. It would be quite hard to do this while the trailer is being used.
I suppose you could also pop the covers on the batteries and do a hydrometer measurement.
For the reasons stated above, most people use a shunt and battery meter of some type.

Wouldn't the shut and battery meter give you the same voltage reading a volt meter?

Yes, they would. The voltmeter is a general purpose tool that EVERYONE should have in their toolbox. I prefer the clamp-on DC meters, as they allow you to measure DC amps without opening up the circuit.
The shunt and battery monitor combination also measure DC amps, but since the shunt is a precision resistor that is always in the circuit, it tends to be more accurate. Also, when measuring current (as opposed to voltage) you get decent readings no matter what the current draw or how long the batteries have sat idle. The voltage reading on a battery monitor has the same drawbacks as a standalone meter, you have to let the batteries rest for several hours before getting an accurate measure of SOC
So, I think in the end it just a question of how much work/money you want to put into it. If you just want to get an estimate of your battery usage. Then using the meter to measure SOC might be good enough, as long as you are willing to let the battery rest for several hours. If you want continuous, accurate, SOC measurements then the shunt/battery monitor is the way to go.