Starter dragging 88 tempo

When trying to start it turns over about 5 or 6 times, each time with less power than you just get a click from lack of power. Good batteries have been tried, same result. Acts just like a low battery. Cleaned all connections, same results. Does start while being boosted. Starter engages fine with boost from running vehicle. Starter shot? Please help!

I think it is shot, sorry bud.