The answer is simple, but it takes a little bit of math to get there.
First of all, the relationship between volts, amps, and watts can be confusing to the lay person. It’s easiest if you compare electricity to water, because you can see water and touch it and it makes a lot more sense.
Volts are roughly equivalent to water pressure, Amps measure how quickly the water is moving, and Watts are a way to describe how much water you’re getting over time.
When you look at the power supply of a cell booster, it’s sure to tell you that it supplies something like 5 watts at 2000mA (1000 mA=1 amp). To translate that into watts, which will really let you see how much power you’re using, use this calculator. It tells you you’re using 10 watts of power, equivalent to leaving one LED light on all the time, or two strong nightlights. Does that seem like a lot to you? When you consider the benefits that a cell booster brings to your home, it’s not that bad.
Energy is billed to you in kilowatt-hours, so to figure out how much money you’re spending to run that cell booster, feed the volts and amps measurements into the calculator to get watts, then multiply by .732 (which is 24×30.5, the rough number of hours in a month, divided by 1000 to convert from watts to kilowatts.) Electricity costs vary from location to location but chances are it’s not much more than a few cents.