I am with Breckman99 on it probably not being the brushes.... if anything,,, and this is only if you had the wrong fuse, or no fuse,ie hard wired, a short might blow the diodes in the Alternator... but that is very slim chance... something would be engineered to give way first unless you were touching the alternator post directly....why not have one gauage of each ? You check the voltage available with the push on switch before you crank the starter (this is sop on aircraft), then you start up and the amp guage tells you the second by second relationship between the battery and the rest of the system.... Greg