From SmartShunt Manual, Section 7.1.4:
The “Tail current” parameter is expressed as a percentage of the battery capacity.
As I understand it, the unit of "tail current" is Amps; the unit of battery capacity is Amp-Hours. A percentage of Amp-Hours is still Amp-Hours.
How does the SmartShunt calculate an amperage from a percent of battery capacity?
Theoretically, the tail current the the percentage of the 1C charge rate of the battery (the current flow required to charge the battery in 1 hour), so if you have 400 Amp-hour of batteries, the 1C charge rate is 400 Amps and if your tail current is 1% then it is 4 Amps. This makes the units correct, but simply it is the percentage of the numerical value of the battery capacity.
What would you set tail current to on 12v. 460ah? Is there some sort of equation for this?
It depends on battery chemistry as well. But the 4% default is a good place to start.
More on Tail current here.
Tail current is 460*4/100=17.6A.
To elaborate on @pwfarnell answer, Amp is actually a rate defined as 1Joule per second at 1 Volt. So the short cut of % of capacity in Ah is logical and consistent and eliminates more complex calculations.
