PORTLAND – Senior citizens who need a little boost on hills and commuters looking to arrive at work without breaking a sweat are turning to battery-powered bicycles.

A small but growing number of the quiet, approximately 50-pound bikes have hit the streets in southern Maine. Store owners and those who service the machines call the riders a mixed bunch.

Some, like Claire Holman of South Portland, are commuters. Seeking fresh air and exercise, she decided to pedal to and from her office at the University of Southern Maine in Portland.

But it’s a sweaty ride up and over the Portland peninsula twice a day, and Holman decided she didn’t want that much exercise.

Her solution: spend about $1,000 for an electric power assist bicycle that takes her over the hills and to the University in 20 minutes. Her bike’s battery recharges in hours and the peppy half-horse engine makes her pedals spin with ease.

“Compared with a conventional bike, commuting with an electric bike is the difference between jogging to work and walking to work,” said Holman, 44. “It’s exercise, but you don’t end up dripping wet.”

Stacy Wentworth, a 63-year-old retired builder from Arundel, bought his bike last summer. Safety was a concern, he said, because his balance is not what it used to be, but the new machine meets his needs.

“It tracks beautifully and it’s stable,” he said. “I pedal constantly but, when I find myself in a tough place and I need a little assistance, I work a lever with my thumb for an assist.”