Low voltage will cause a DC motor to slow down. On a bow thruster, it can cause the solenoids to freeze up. Kind of like your car, sometimes hammering on 'em will help, on my Vetus I had to stick my finger down the hole to loosen it. Yes, I did tell it that it may experience a little momentary discomfort.
"There's the Right Way, the Wrong Way, and what some guy says he's gotten away with"