Refrigerators & Freezers Results : ENERGY STAR
You can see what a brand new energy star rated chest freezer uses, 408kwh per year is not great if it was brand new, it's costing you about $50 per year to run, but if it's older then it's most likely not using much more then it was designed to use.
To get it to use less you can defrost the inside and you can vacuum out the compressor area, also make sure nothing is pressed up to the outside as that is often where the outside coils are and you need air flow.