I can't start my car. The starter turns over very slowly and weakly. (I noticed the starter turned over slowly a few days ago, when I last started it, but it started; now it won't start at all). Interior lights come on. I've not tried the main headlights, for fear of draining the battery. The battery measures 11.5 volts (it's a few years old). Do you suspect the starter (or possibly solenoid, if it has one)?