Explanation of the Charge Status as displayed by SmartGauge
The Charge Status as displayed by SmartGauge is not directly related to the available amp hours remaining in the straightforward manner that may be expected.
This is because SmartGauge displays the charge status as a percentage of the total available energy in a battery as opposed to the total available amp hours. They are not quite the same thing.
The remaining energy available in a battery is not only related to the available amp hours remaining. It is also dependant upon the battery voltage.
For instance. Suppose you are using an inverter (let's assume the inverter is 100% efficient for ease of calculations) to power a 100 watt light bulb. The batteries are fully charged. The battery voltage cannot be calculated because it depends upon too many variables. But let's take a guess at around 12.5 volts when powering the inverter and lightbulb.
At 12.5 volts, with our 100% efficient inverter and 100 watt lightbulb the current draw on the batteries will be 100 watts divided by 12.5 volts = 8 amps. So in 1 hour it will use 8 amp hours.
Now come back to the battery some time later when the battery has run down in charge status. The battery voltage will have fallen somewhat. Let's guess it at 12.0 volts. The inverter is still powering the same load with the same power but the battery voltage is lower. So in order to maintain the same output voltage the inverter will draw more current. Now the current draw on the batteries is 100 watts divided by 12.0 volts = 8.3 amps.
So with the batteries in a lower state of charge, in 1 hour it will now use 8.3 amp hours. But we have been powering exactly the same load with exactly the same amount of power.