Will the alternator affect the performance?

While a vehicle engine is running the alternator generates electricity to run the car and operate things like the radio, power windows，seats，doors，wipers，and the spark plugs to ignite the fuel making the car go. The excess electricity recharges the battery which is primarily used to start the car in the first place. Without the alternator your car will only run off the battery which will eventually run down and wear out much quicker and need to be replaced. As the battery is dieing its efficiency degrades affecting your performance until it fully dies then your car will not go.