In the 19th century, were electric bills measured in ampere-hours, not kilowatt-hours?

PSNH has launched a very cool Tumblr feed with historic photos and other old stuff - it's a lot of fun.Check it out here.

But I'm puzzled by an 1897 bill from Hillsboro Electric Light and Power Co., which charged the customer based on usage measured in "ampere-hours" rather than the "kilowatt-hours" used today.

I wonder if that unit of measure was common at the time, and if so, why? Perhaps it was DC power, since amp-hours seems to be a measure used in batteries; the AC-vs-DC fight over power standards was far from settled then.