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Can I recharge a dead car battery?

Tom Vondrasek | 6th May 2023 | 5 minutes to read

If you have driven a vehicle for a number of years, most of us have experienced that sinking feeling of turning the ignition key and getting a click noise or a starter motor sounding like a teenager being asked to get out of bed early. Both are sounds you don’t want to hear, and it usually happens on a freezing cold morning just to brighten up your day.

The most common cause is a battery that has run out of charge. Naturally you try it another 10 times in the vain hope it will do what it is supposed to while swearing or pleading with it to start.  Eventually the verdict is you need to do something about the battery.

Here are some of the reasons you might have a flat battery and how to fix it:

  1. Possible Causes of a Flat Battery
  2. Courses of Action
  3. Charge the Battery Using a Battery Charger
  4. Battery Still Going Flat?
  5. Choosing a Battery Charger
  6. Where To Buy a Battery Charger

Possible Causes of a Flat Battery

Before taking action, it is worth trying to work out why the battery is not working, as different reasons have a different course of action you can take.

  • User Error – Battery was working fine until you left the lights on or a door or boot open overnight which drained the battery.
  • Old Battery – Battery is over 4 years old and starting the car was taking longer.
  • Temperamental – Starting the car occasionally took longer than normal or sounded different.
  • Reason Unknown – Worked fine and now is suddenly not working.
Image of car battery charger

Repco offers replacement batteries, jumper leads, and battery chargers to save you from the woes of battery trouble.

Courses of Action

To get you going here are three different approaches to fixing your battery depending on your circumstances.

Replace the Battery With a New One

In the case of an old battery or a temperamental one, a full replacement is often the best solution.

Batteries have warranties and once out of the warranty period, replacement is a good option — especially if you rely on your vehicle and the warranty period expired over a year ago.

If the battery is maintenance-free, it should have a charge indicator light which can help your decision. You can also try recharging it as most good battery chargers will tell you if the battery can handle it or if it is too far gone.

Jump Start the Vehicle Using Another Vehicle or a Portable Jump Starter

Battery charger with jumper leads

This is the quickest way to get your vehicle going if it is user error or a temperamental battery, and it’s a good starting place if the reason it stopped working is unknown.

As a precaution, take the jump starter or jumper leads with you as you may still need them. Once started you need to make sure you are driving the vehicle or running the engine for at least 15 to 30 minutes to try and get some charge back into the battery.

Before jump starting check for loose or badly corroded battery terminals as this could be causing the issue. The cables should be clamped solidly to the battery terminal and not wiggle when moved. If they do, tighten them.

Corrosion looks like a white or bluish-green tinged fungus growing on the terminals. It is best removed so you can inspect the terminals for damage as, being acidic, it eats them away. Do it out on a driveway as it involves cleaning with water.

Carefully pour near-boiling hot water over the terminals to dissolve the corrosion. It pays to flush around the sides and bottom of the battery with a cold-water hose on low pressure to make sure you rinse off all the corrosion.

Water neutralises the acid. When cleaning off the corrosion, wear gloves, safety glasses, closed-toed shoes, and old clothes. Being an acid, it is not good for eyes, skin, and clothing.

Charge the Battery Using a Battery Charger

Car battery recharging car

This is the slowest fix as to fully charge a battery takes hours. A modern battery charger will let you know if charging the battery is worth it or not. If you are only doing short distances every day, like a few kilometres, this will slowly kill the battery as it is not long enough for it to recharge. If this is the case, then charging the battery with the charger may need to become routine. Once fully charged you know your battery will be OK.

Some modern battery chargers struggle to charge a dead flat battery if the voltage in it is too low. It needs to detect a certain voltage to kick start the charge process. You can trick it by putting a 9V battery across the terminals (positive to positive, negative to negative) and once it starts off, you can remove it. It is enough to trick the charger into starting its charge process.

Battery Still Going Flat?

If you are still having issues with the battery going flat after taking action to fix it, then there are 2 culprits that can be causing the issue.

  1. The vehicle's alternator or charging system that keeps the battery topped up has an issue and is not working correctly. This is easy to check as a lot of the new battery testers can also check the charging systems on vehicles. Your local Repco store may be able to help as well, otherwise contact your local workshop.
  2. Parasitic drain is when something electrical is draining power from the battery when the vehicle is switched off. The problem with modern vehicles is a lot of items use minimal battery power when the vehicle is turned off. Identifying the cause may not be easy and you may need to use an auto electrician to identify the source. I am not talking about user error where you know you left something on overnight. This is where everything has been turned off and the battery is still being discharged at a rapid rate.

Choosing a Battery Charger

It is always good to know the capacity of the battery in Ah (Amps per hour) and the the battery type before purchasing a battery charger. If you have multiple vehicles, you need to check all the batteries and see if you can get a charger to work on all of them. It is also a good idea to get one that maintains batteries so you can move it around vehicles that are not used that often. It may be more expensive though the benefit of being able to start your vehicles when you need them is a real bonus.

Where To Buy a Battery Charger

At Repco we have a great range of battery chargers to suit your needs and budget. Everything from a small charger to do your 50cc motor bike to charging your diesel Ute battery or keeping your caravan deep cycle battery in good shape. Shop online or in store and keep an eye out for our specials. If you’re not sure, contact our friendly store staff before purchasing your battery charger.

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