Car batteries: How to choose, charge and change them
Car repairs and maintenance can easily become a huge expense with recent research finding that drivers are spending an average of £574 yearly on car repairs, taking the national total to £21.5 billion (Green Flag). And, with more complex technology and smart features being implemented in the design of new car models, it’s only a matter of time before this rises again.
While some car repairs will need to be done by professionals, there are many simple maintenance tasks and repair work you can do yourself. This can include something as important as dealing with the electrics that start your vehicle — like the car battery. Here, we will be showing you how to charge and change your own battery, which should save you both time and money. We’ll cover:
- Why do car batteries run down?
- How to check your car battery
- How to charge your car battery
- How to change your car battery
- How to keep your car battery running longer
The signs of a dying car battery are never good: your headlights will get dimmer, your engine won’t turn over, and you'll struggle to get anywhere in a hurry. There are a number of reasons why car batteries can run down. For example, if:
- You’ve left something open or running
Making a mistake, such as leaving your boot open or headlights on, can put a lot of strain on your battery and guzzle up its supply of electricity. The simplest fix is to ensure all doors are properly closed and that nothing is left on when you leave the car. This is especially important if you have kids who might not have pushed the door hard enough when leaving your car.
- Your parasitic drainage is exceeding normal levels
A common misconception is that, once you take the keys out of your car, the vehicle’s electrical supply is cut off. But every car has what is referred to as "parasitic drain": enough of an energy supply to keep electrically-powered elements like the clock, radio, and alarm operational even when the car isn’t powered. If there is an electrical problem such as faulty wiring, this can mean the parasitic drain exceeds what is normal and depletes the battery quicker.
- Your battery is old
Your battery should be changed every 3–4 years so, if yours has exceeded this and your car isn’t functioning as it should be, it could be a sign that your battery is worn out. If you ignore this, it’s likely that your car battery won’t be able to fully charge and may die regularly. If you find this is the case, it may be your best bet to replace your car battery — we stock a range of car batteries so you’re bound to find a suitable one for your car model and make.
- You’re travelling short distances too frequently
Your battery outputs the most energy when you’re starting the car. So, if there is too little time between this and it shutting off again, the alternator may not have enough of a chance to recharge meaning it dies more often or can’t last as long.
- There are damaged or loose battery cables
Your battery won’t be able to charge properly if the cables are damaged. To preserve these, you should be checking them for signs of damage or any dirt every couple of months or so, and cleaning these out with a toothbrush or dry cloth. Faulty or loose battery cables can also make it difficult for the car to start, as there won’t be enough electricity being transferred to the engine.
- Extreme temperatures are making it fail
Although hot or cold temperatures can’t kill your battery completely, they may cause it to fail. As a result, sulphate crystals might begin to build up, which can have an impact on the long-term battery life. Plus, it can be harder to charge your battery in these temperatures.
- Your alternator has a faulty diode
The car alternator recharges your car battery and powers things like your lights, radio, and windows. If the alternator diode or rectifier fails, then the alternator output will drop to such a low level that it will be unable to charge the battery, and the battery warning light will come on. If you’re in need of a new car alternator, make sure you check out our range, where you’ll find one to suit your car, whatever the model may be.
Generally, your car battery will last about four years, but it should be checked at least twice a year. And, although this will be done when your car goes in for servicing or MOT checks, there’s no reason why you shouldn’t also be checking your car battery yourself.
PLEASE NOTE: For warranty purposes, a professional battery test report is required to indicate full health of a battery and any faults.
There are a couple of worn battery indicators you should look out for, including:
- Powdery residue on the battery terminals
- Battery warning lights on the dashboard
- The engine taking longer to start, especially in extreme weather conditions
- The dashboard displaying the check engine light
If you have experienced any of the above or have an inkling that your battery is worn, there are measurable checks you can do to find out if this is the case.
Most car batteries will have a charge indicator on the top, which will show you how the battery is functioning. If the charge light is showing green, it means your battery is fully charged and working well. A yellow dot will indicate a problem with your car battery, while there will be no light if you need to use your car battery charger. If you don’t already have one in your kit, make sure you browse our range of car battery chargers to ensure you’re prepared the next time you encounter a problem. To check your car battery, you’ll need a voltmeter or multimeter, as shown in this video from ChrisFix:
- Always test your car battery after it has been left overnight to gauge your car’s resting voltage and overall health. This is important as, if your vehicle has recently been for a drive, it might give higher readings that are misleading.
- Locate the battery. It’s usually fitted in the engine bay at the front of the car and on either side of the engine.
- Make sure you can access the battery terminals on your own — some may require more help to get to. These are sometimes protected with a plastic cover that will unclip or need to have bolts removed.
- You’ll want to measure the DC (direct current: the electrical charge that flows in only one direction) voltage. To do this, set the multimeter dial to 20 to gain an accurate measurement between 0–20 Volts.
- Many meters come with a red probe and a black one, too. The red probe should be held to your battery's positive (+) terminal and the black probe to the negative (-) terminal.
- Check the reading. A fully charged battery will have a reading of around 12.8–13.9 volts, while ones with readings of 12.4 volts are about 50% charged and flat ones will show readings of 12.0 volts. If you get a reading with a minus sign in front of it, you’ve got the probes the wrong way around.
If you think your battery may be experiencing excessive parasitic loss, you can either remove the battery leads or remove the battery from the car completely. After this, you can use a car battery charger and then test it at least 12 hours later. If the battery is holding charge when it’s not connected to the car, something other than your battery and alternator may be causing the issue.
How to test for dead battery cells
Battery cells can die, which could prove problematic as the car may appear fully charged but won’t function as such. To test for dead battery cells, you’ll need to buy a hydrometer battery tester, as this can measure specific gravity or battery acid and indicate whether there are any dead cells.
It might seem complicated if you’ve never done it before but charging your own car battery can save you both time and money, so it’s well worth learning how to do it. Battery charge times can vary for different models and makes, as well as be affected by the battery’s amps and the exact charger you’re using. We recommend going for a lower charging speed (around 2–3amps), as this will reduce the chances of the battery plates buckling.
This tutorial from ehowauto shows how simple the process can be done at home:
- Inspect your car battery and look at the charger you are intending to use to see if they are compatible. If your car has a stop/start function, it’s likely to have an AGM/EFB battery that will require a smart charger. This will be able to detect fast charging modes and reduce the amount when the battery is full to prevent over-charging. For most other batteries, a conventional charger will do, and there are even more eco-friendly options like solar chargers available. If you’re still not sure, it’s worth visiting a motoring supply store for advice — we have over 70 branches in the UK, so find your nearest one here.
- Check the lead terminals that are connected to the top of your battery, as well as the clamp that connects them. These will need cleaning before you use your car battery charger.
- Disconnect the battery one lead at a time. You should always disconnect the negative (black) cable first and reconnect it last to prevent electric shocks. The terminals are usually connected to a battery with a bolted clamp, so you’ll need to unscrew these first. Disconnecting the battery can reset your radio and dashboard settings, so make sure you have your security codes to access them again (these can usually be found in your car’s handbook).
- Connect the clamps of the charger to the terminals on the battery — match positive with positive and negative with negative. Try to keep the charger as far away from the battery as possible for safe charging.
- Turn on your car battery charger and be sure to find out whether it will automatically turn off when the battery reaches full capacity or if it’ll need disconnecting. This equipment will usually come with a manual with details of how long it’ll take to charge your car battery and any other specifics you’ll need to know.
- Disconnect the clamps when the battery is fully charged and reconnect the car battery (making sure to attach the positive lead first and then the negative one).
In most cases, installing a replacement car battery will only take you around half an hour and will only cost you the price of an adjustable spanner. First things first, you’ll need to assess what car battery you need — if you can’t tell yourself, experts at a garage or parts supplier are sure to be able to help — we have a tool that lets you input your car’s registration and information so we can help you find the battery you need. Once you’ve got the right battery and the necessary tools on hand, you can remove the old battery safely to make way for the new one.
Removing your old car battery
Although a relatively simple procedure, disconnecting your old car battery can be hazardous if you don’t follow the advice associated with the process.
- Locate your battery and remove the bolts that are holding the battery bracket.
- Make sure there are no leaks or damages to the casing, as this will require professional attention.
- Disconnect the negative (black) lead from the battery terminal first using the spanner to unscrew the nut on the black lead’s clamp, and then do the same for the positive (red) lead.
- Tape the ends of the lead with duct or insulating tape. This will ensure the leads won’t touch or rest on conductive metal like the car’s body. We stock a selection of adhesive tapes that’ll be perfect for this.
- Lift the car battery out of the engine bay — there may be a handle to help you with this.
Fitting a new car battery
Fitting a new car battery is very similar to the removal process, with some necessary precautions to take when installing your replacement:
- Place your new car battery into the battery bay and remove any plastic caps on the top of the terminals.
- Connect the positive terminal by pushing the red lead onto the positive battery terminal and tightening the bolt to the clamp.
- Repeat for the black lead and the negative battery terminal.
- Replace the battery retaining bracket and the plastic cover if necessary and secure the bracket with the bolts you removed at the start.
Check out this video from Ask The Mechanic to see how it’s done:
Batteries, old or new, are made using strong acid as well as heavy metals and other non-degradable materials. So, you’ll need to take measures to reduce the chances of potential chemical spills or injuries from weighty elements from becoming a reality. We advise taping over the old battery terminals with insulating tape to ensure the two leads don’t react together and be sure to transport the battery the right way up to prevent any leakages.
Your local council will have a specific disposal service for hazardous waste, so make use of this. You can find your nearest point on the government website.
Although every car battery will need charging and replacing at some point, there are things you can do to get the most life out of yours:
- Park in a sheltered space: If you’ve got the space and facilities, parking in a garage can ensure your vehicle isn’t exposed to any extreme temperatures, which can interfere with the battery functioning.
- Don’t leave things plugged in: Although charging your phone won’t cause destructive amounts of energy drainage, leaving your charger plugged in overnight may still cause power drain even when the car isn’t turned on.
- Keep your battery terminals clean: The servicing team who take care of your car are bound to do this for you, but you should inspect your battery terminals for any signs of build-up that’ll need removing as often as you check the fluid levels in your car. You can get rid of this by disconnecting the battery from the car and sprinkling baking soda onto the terminals and pouring a couple of tablespoons of water on top of this. Then do the same on the battery cable ends and scrub these and the terminals with an old toothbrush. Finish by rinsing these with a little bit of water and let the battery dry completely before reconnecting the parts. Be careful not to drown the battery or electrics in water as this could break them or create a dangerous situation when you go to plug them back in.
- Inspect your battery regularly: Quick visual inspections can give you the opportunity to spot any problems that need to be addressed before things become unfixable or dangerous. So, it’s important to check for any signs of bloating or wear every few months to keep the condition of your car battery under control.
- Secure it properly in the bracket: If your battery is not secured, it may vibrate excessively, which can cause internal damage and short circuiting. To ensure this doesn’t happen, check your battery bracket every couple of months to ensure it’s tightly positioned and secure.
- Test your battery often: Testing your battery with a multimeter/voltmeter at least twice a year or more will give an indication into how well you’re maintaining your battery. Plus, it’ll ensure you don’t get caught short if you’re due a new one.
There’s never a good time for your car battery to die. So, it’s always good to know how to monitor your battery and the maintenance tips that will help it to last as long as possible. Whether that means knowing when and how to change it, clean it or charge it, we hope this guide has answered all of your queries.
Here at GSF Car Parts, we stock an impressive range of car parts for many makes and models, so you can find the right replacement and maintenance equipment for your vehicle. Plus, as we offer free UK delivery, we make sure you can save money while getting everything you’ll need to keep your car running better for longer. If you want to find out more about maintaining your car, why not check out our knowledge hub? We have troubleshooting advice for a range of issues, so you can save unnecessary time and money on your car repairs. If you have any questions about our parts, don’t hesitate to contact us, or call us on 0121 626 7971.