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How to charge a car battery at home

Charging a car battery

Why won’t my car start? Do I need to recharge the battery? 

Trying to work out why a car’s engine won’t start involves making your way through a checklist.

If the engine turns over strongly but won't start, the battery isn't at fault. Immobilisers are often to blame for this issue, and sometimes a fix is as simple as locking and unlocking the car and trying again.

If you turn the key and the car's completely dead – no warning lights on the dashboard and no noises coming from the engine bay – check to see if the headlights were left on the last time you used the car; lights can drain the battery in as little as half an hour.

If everything checks out make sure the battery terminals aren't loose. 

If you're sure the battery is to blame, and jump-starting isn't possible, you'll need to charge the battery. 

How is a car battery charged?

  1. You can connect a Halfords car battery charger (other retailers sell them, too, from £20). You can either do this with the car battery in situ, or you can take the battery out first
  2. Battery chargers are fairly self-explanatory: connect the '+' and the '–' to the battery terminals and turn the charger on. Most have lights to tell you the state of charge and when the battery is full.
  3. If you remove the battery from the car, don't charge it in the house – a faulty battery (or charger) can potentially cause an explosion and/or a fire.
A trickle charger for a car battery

How do I keep a car battery charged while in storage?

If your vehicle spends time sitting around not being used, especially during the winter months when you may have declared it SORN, a trickle charger (or conditioner, as shown above) may be a better option. It actively monitors the battery's health and can remain connected for extended periods because it only adds charge when it's needed.

Learn more about a battery's amp-hour rating and what it means for its operating life.

Testing a car battery with a multimeter

How to test a car battery with a multimeter

  1. You can do a simple battery test with a basic multimeter (buy them for around £20). Turn the dial onto the '20V' setting and connect the red probe to the '+' side of the battery terminal and the black probe to the '–' terminal. 
  2. It will then give you a voltage reading. '12.6v' means there should be sufficient power to start the car, so if it's not starting and you're reading 12.6v then the battery isn't at fault. 
  3. If the reading is lower, then you may experience issues, and if it's any lower than 12v it's technically flat, so starting will be virtually impossible and you may need to start thinking about car battery replacement. 
  4. With the engine running the voltage should read between 13.8v and 14.4v.
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