Signs of a Bad Altenator

• A bad alternator cannot effectively replenish a battery power supply.Hemera Technologies/AbleStock.com/Getty Images
  
  The symptoms of a bad alternator can initially mimic those of a dead battery. This can cause some drivers to replace the battery without realizing the root cause. Misdiagnosing an alternator problem can cause a vehicle owner to replace multiple batteries as the defective alternator simply drains each new battery of power.
  
  

Rapidly Draining Battery

• A failing alternator is not able to replenish the vehicle battery charge, while the car is operating. This results in a rapidly depleted battery charge, which leads to a no-start condition. The battery will not be able to maintain a charge, even when it's jump-started. A vehicle with a bad alternator may respond to jump-starting and may initially operate as normal. This won't last for long, as the vehicle will stall the first time it is in an idle position due to the lack of charge regeneration.
  
  

Persistent Check Engine/Check Battery Light

• A vehicle that is experiencing an alternator problem may illuminate its "Check Engine" light during start-up and keep the light on during vehicle operation. The check engine light usually glows yellow and is often located on the dashboard. The vehicle electronic control module may also turn on the "Check Battery" light, as it detects a problem with the battery charge levels. This light glows red and indicates a more immediate alternator/battery problem, such as a lack of sufficient voltage to keep the vehicle running.
  
  

Over-Charged Battery

• A malfunctioning alternator may actually produce too much voltage and overcharge the battery. Symptoms of this problem can include overheating of the alternator, burned out light bulbs from power surges and damaged battery plates. An alternator that consistently overheats will display damaged internal components, resulting in a need to replace it. The battery may also be damaged through overcharging, along with connectors and wires running from the battery to the alternator.