All inverters have an idle current
. What the current
is depends on what tricks the inverter has. Some have a fixed fan that goes all the time for instance. So you are paying(with power use) the price
of runnign the Fan. Some have a thermostat controlling the fan and some the fan comes on with current draw. Some inverters are running an output all the time. I mean by that, they have the output voltage present with a load or no load. That means they have a small amount of current consumption
going on all the time. Soem inverters have a load sensign start up feature. So they have less consumption
when no load is applied. For instance, my Freedom 25
is 0.4A idle, no output(no load) and 0.9A idle with 230V output(non load).
As to efficiency, some inverters are more efficient than others are producing the outout. But one of the big inefficiencies is the actually waveform produced. A pure sine wave has more "power" in it than a modified sine wave. There are inverters that produce better modified sines waves than others. That usually is reflected in the cost of the inverter. You can make cheap
inverters these days, but they don't always perform that well. Problem is, you won't ever really know. unless you have two inverters side by side. One good, one nasty, but both of same recomended output. Plug
them into a seperate battery
identical loads on each. Say an electric
kettle. Then time how long it takes to bring the kettle to the boil. Measure the amount of energy consumed from each battery
. In most cases, the ncheap and nasty would have required more energy to do that same work.