A loose alternator belt will affect the alternator's performance and will lead to automotive electrical failures, such as dead or weak batteries, dimmed headlights and engine stalling. Common signs of loose alternator belts include a loud squealing sound, improper voltage and flickering gauge lights, according to Pep Boys.
Since alternators are powered by automotive engines via fan belts connected to crankshafts, a loose belt can cause the alternator to undersupply the car's power requirements and drain the battery until the charge runs out. Loose alternator belts also cause automotive components to work harder in order to compensate for voltage fluctuations. Eventually, the slack leads to belt fraying and premature wear out.