A homemade battery pack on an e-bike was the likely cause of a fire at a 100-unit apartment building in South Portland Friday morning.

The fire department was alerted to the fire at 425 Broadway by the building’s automatic fire alarm and sprinkler system at 7:37 a.m. Firefighters who arrived on scene three minutes later found significant smoke and an e-bike on fire in a seventh-floor apartment, city officials said.

The resident of the unit had already gotten out of the apartment and firefighters evacuated the rest of the building. One person was evaluated for smoke exposure, but refused treatment. There were no other injuries to residents or firefighters.

Investigators determined that the fire was likely caused by a homemade battery pack that was used to replace the original battery pack on an e-bike stored inside an apartment.

“SPFD would like to emphasize that devices like e-bikes should not be left to charge or generally be stored inside a living space,” city spokesperson Shara Dee said in a statement.

Lithium-ion batteries store a large amount of energy in a small space and when damaged or used inappropriately, can overheat, catch fire or explode, Dee said.

Hazard Towers, also known as 425 Broadway or Broadway East, has 100 units and is operated by the South Portland Housing Authority. After the fire was put out, staff from the housing authority determined five units were unfit for occupancy. The housing authority will provide temporary accommodations for displaced residents.

Broadway near the Cottage Road intersection and surrounding side streets were closed while crews were on scene.

Crews from Cape Elizabeth and Portland assisted at the scene, while Scarborough and Westbrook provided station coverage.