How to calculate amp load based on watts for 12v system?

[SunSeeker1]

My 230v inverter shows the load of the fridge plus fan at 140w. If I want to calculate how much amps this load is drawing from the battery do I do 140 divided by the pv voltage (eg 16v) or by the battery voltage (eg 13.1v) or just by 12v?

I know the load is 140/230 = 0.6 amps but I want to figure out how much is being sucked out of the battery.

[Mike90250]

AC watts * 1.2 (80% efficient inverter) = DC watts so 140 *1.2 = 168dc watts / 13.1v = 12.8 amps dc or something pretty darn close

I used your battery voltage, but generally, I would us the baseline bank voltage 12V and build a little extra bit of margin into the calculation.

[SunSeeker1]

AC watts * 1.2 (80% efficient inverter) = DC watts so 140 *1.2 = 168dc watts / 13.1v = 12.8 amps dc or something pretty darn close

I used your battery voltage, but generally, I would us the baseline bank voltage 12V and build a little extra bit of margin into the calculation.

So which is more accurate to use battery voltage or system voltage with a margin of error (what's the margin exactly?)

[Sunking]

Nominal battery voltage is what you want to use, 12 volts. You want to use worse case. Electrical we measure with a micrometer, mark the spot with chalk, and cut with an axe.

[littleharbor]

Fire up the diesel generator to charge my flashlight batteries.