How do you discern between a battery (When the vehicle is started) that can't keep 13-14v and an alternator that isn't charging it properly? (Assuming bad cables/ground/etc is out of the way)

Can't voltage below 13-14v be a symptom of both a bad alternator OR a battery on its way out due to refusing charge?

What is a good way to discern between the two?



If you have started the engine and you are getting 13-14.5V, the alternator is working and your problem would be most likely battery. Your local auto-parts store will usually have a heavy discharge battery tester to prove or disprove the servicibility of the battery before laying out money to replace it. In passing you should not assume the cables are OK but they should be checked so that they are known to be OK. A consideration if a battery is not holding a charge is a parasitic drain, this is to say that even when the system is turned off a component or system remains on. An amp meter in series with the battery earth cable will reveal this.

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