I have a 9 year old el cheapo Tower Hobby low end starter that I immediately converted to on board NiMH 8.4 batts in series...16.8 volts DC
Once a year I discharge and recharge the bats....Trigger good, cone good, instant start good if I prime properly...Run time in last nine years assuming a less than 15 second use is still under 5 hours.... Hell I have several makita, deWalt, Black n decker, Cobalt and porter cable batt powered tools some over 10 years old with no appreciable commutator or brush wear....
I am a tool nut and a electrical genius.... My flying club has 50 members with Sullivan starters...for some big honking gas engines.... every one I diagnosed had LOW bat power, or Bad contact switch, OR broken wires in the Bat to starter line.....
Frank...explore the contact switch first for corrosion...then connections for bad solder or broken conductor...AFTER assuring a full 12 VDC or higher source...if all good open and look at the brushes....but in my experience the compounds used now in Carbon brushes and polished commutators show very little wear