Faulty Battery or a Faulty Alternator ?

How to determine the difference between a faulty Battery or a faulty Alternator

Usually the first indicator is when you come to unlock the doors via the remote central locking and they won’t open. This is usually an indication that the battery may be flat. Once you put the key in the ignition and turn the key you will notice that some warning lights will display on the dashboard. If you turn the key to start the car and nothing happens you more than likely have a dead battery or a starter issue.

It is quite common for people to assume that something other than the battery is the cause because other things in the car are still functioning and performing as they should such as the headlights will still work. A standard car battery is meant to have between 12.4 volts and 14 volts in order to perform efficiently.

Lights only require 6 volts to perform, which is less voltage than what the starter needs. In order for the starter to perform it requires at least 9 volts, anything less and the starter won’t work If the voltage is 9 volts or above the starter will kick in and try and start the car.

So how do you tell if you have a dead battery?

  1. Remove the key from the ignition
  2. Open the bonnet
  3. Check your connectors, red for plus and black for negative

On the positive red side there will be a + symbol and on the negative there is a minus – symbol. The first thing to check for is that the connectors are tight. If there is any movement at all when twisted with force this indicates a poor connection and will not send enough power around the car in order to start.

If you battery is drained down too far or it has bad cells you may not be able to jump start the car and keep it running. Common batteries have six cells, three are located on the left hand side which is the positive and three on the negative side the minus. If any of those cells are bad you may get a reading that the voltage is good enough but as soon as you try and start the car it will drain tremendously.   Each bad cell means that you have less cold craning amps.  Cranking amps determine how much power you have to start your car in most climates. a battery in a cold environment (0°F/-18°C) and measure the discharge load in amperes that a new, fully-charged battery can deliver for 30 seconds, while still maintaining terminal voltage equal to or higher than 1.20 volts per cell.

If a car battery needs 600 CCA and has three bad cells it will only produce 300 CCA which isn’t enough to start the car. So even though there is good enough voltage because of the bad cells it isn’t good enough to perform under a load.  If you have no way of testing it, remove it and take it to a good motor factors for them to test and replace if necessary.

Alternators don’t cause faults that often and are more expensive to replace than a battery.  Usually you would get 150,000 miles on average out of an alternator. If the car starts after a jump start and continues to run the alternator is working fine and charging the battery.

If the alternator was dead or bad you wouldn’t be able a drive for a few miles after a jump start.

Another way to tell if the fault is battery related rather than alternator related is the lights on the dashboard. If the battery warning symbol displays or the charging management light displays you will need to refer to your owner’s manual to understand what could be causing these lights to display.  If you get a battery light the battery is bad. If you get a charging warning light your alternator is more than likely bad.

Battery starts the car not the alternator, so if you have problems starting your car the battery is weak. Maybe the car hasn’t been driven in a while. Maybe the car isn’t being driven enough.  To keep the battery performing you will need to drive the car at least once a week but daily is better. Typically a good thirty to sixty minutes of driving will keep the battery charged.  If you commute in shorter distances such as ten minutes to work for example and ten minutes home or simply just using your car to commute to the shops and back you could wear a battery down in sixty – ninety days.

If your alternator packs in you may have enough power in your battery to get you to your nearest mechanic . It is best practice to turn off your radio and driving lights during the day and save as much power in your battery as possible to get you to your nearest specialist.

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