What can cause my battery to drain?

What is causing my battery to drain? 

There are many reasons your battery may be draining. The four most common reasons are the battery may be old, a parasitic drain, faulty charging system, or a bad alternator diode. When your battery is showing signs of the battery draining, call us at Bob's Main Street Auto & Towing to have you look over your charging system. 

Faulty Charging System 

If your vehicle has a faulty charging system, it may drain the battery while the vehicle is running. The alternator on the vehicle may not be putting out enough voltage which will allow the battery to drain quickly. The headlights and radio will stop working and the vehicle will no longer start when the battery drains. 

Old Battery

We recommend replacing your battery every four to five years. Old batteries that have been drained completely are unable to hold a full charge. 

Bad Alternator Diode

A good alternator diode allows the current to flow in one direction. When the alternator has a bad diode, it may allow the current in the opposite direction. If the current flows in the wrong direction, it may keep the charging system on after the vehicle is off which also cause the battery to drain.

Parasitic Draw

The most common cause of parasitic draws are head lights, trunk lights, or glove box lights that do not turn off when all the vehicles' doors are closed. Relay switches within your vehicle may also be stuck in the "on" position causing a parasitic draw. 


Call us today if your vehicle is having battery issues. Our auto mechanics are always ready to tackle any repair! 


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