The phrase "to replace the alternator" means to remove a faulty or broken alternator from a vehicle and install a new one in its place. Full definition
The car ran fine for about a week after replacing the alternator and now it won't start. (mechanics.stackexchange.com)
The Corvette Racing crew replaced the alternator in six minutes, losing a lap to the leader. (corvetteracing.com)
New for 2019 is the adoption of hybridization, which replaces the alternator with a motor / generator unit that feeds energy to a 48 - volt lithium - ion battery pack. (skylandchryslerjeepdodge.com)