The 10 surprising car faults that can be caused by a weak battery

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Modern cars are laced with electrical circuits, screens, and complex computer systems. And with all this tech trickling around, it's quite common for some sort of issue to occur. 

It could be a warning light, it could be a strange mechanical malady, or it could even be a crippling issue with the locking system. And, surprisingly often, it'll be down to the car's battery. 

Even in relatively old cars, over 20 years old in some cases, that flickering warning light, or the problem you're facing with the locking system, could be down to bad battery health.

As a car's 12v starting battery reaches a certain point of degradation, it will be putting out a lower voltage. And if one of the circuits, sensors, or motors detects a lower voltage than normal, the problems can start. 

It might be as trivial as a warning light flicking up on the dashboard, but it could be as serious as dim headlights, weird window movements, or door solenoids not responding properly. 

As a rule, if you experience some sort of issue with your car, and you know there's a chance your battery may be getting old, or if it could be low on juice because it's been standing for a while, there's a very good chance that's your issue - rather than a catastrophic engine issue developing. 

The sorts of problems you can see happening when your battery is low on voltage can vary massively from model to model, but here's a rough guide of what to look out for. 

Ten issues you might experience if your battery is starting to die

1. A slow crank, or not starting at all

OK, the first one's obvious. If it's taking longer than normal to start your car when you're turning the key or pressing the button, that's a sure sign your battery needs attention. But it could also serve as a warning that one of the following problems might be about to arise. 

2. Weird warning lights

A weak battery can wreak havoc with all sorts of sensors, and this could mean you're very likely to see an orange "check engine" light appear on your instrument cluster as the car records a fault. 

It's important not to dismiss this warning, even if you're confident it's caused by the battery, as there could be something more serious going on, but if you're battery's on the way out, it's quite likely to be the cause. 

3. Dim headlights 

As the alternator struggles to feed power back into the depleted cells of the battery, one of the signs might be dim or flickering headlights. Obviously, this is not a good thing at night, and it's something you might not notice in the daytime, but it can happen. 

4. Air conditioning malfunction

Of all the electrical systems in a car, the air conditioning system is one of the most power-hungry. So don't be surprised if you experience some sort of issue from a bad battery. 

5. Power steering feeling sluggish

In most cars, power-assisted steering is driven by a large motor, and this is another thing to start suffering if the battery voltage takes a tumble. 

This can be one of the more alarming symptoms, but you're not going to lose your steering altogether, it might just feel heavier, or the assistance could be lumpy and uneven. In some cars, it will be accompanied by a warning light. Just to make your day even worse. 

6. Infotainment systems misbehaving

The central screens in cars now perform so many functions. Way beyond just giving us access to radio stations and sat nav, they can control most driver comfort aspects, and more. 

If these are affected by low voltage, lots of issues can occur. None of these are likely to have a lasting effect, but they could be a bit of a pain. 

7. Fuel system inefficiency

If your battery's low voltage has affected one or more sensors, there's a slim chance it can have an effect on the engine's efficiency. 

This can, in rare cases, mean the delicate fuel and air balance is disrupted, and your car can be running rich, or lean. And this can lead to reduced MPG. 

8. Spark plug problems

Particularly in older cars without systems to balance voltage out properly, a weak battery can lead to a weak spark going into the cylinder. And that, obviously, will cause the car to run poorly. Or even struggle to start at all. 

9. Locking system issues

Cars can use a variety of mechanisms to operate their complex locking systems, and a low battery can affect these in a variety of ways. For example, your car may unlock, but then instantly lock again, as the motors or hydraulic units struggle to complete their cycle. 

There could also be immobiliser issues if a sensor isn't happy, and it's not uncommon at all for the alarm to trigger. 

10. Permanent damage to your battery

If you've had any issues with your car caused by a low battery, even just a slow crank, and if it's the usual lead acid type of battery, it's likely you're on borrowed time. Depleting it below a certain level will cause it long-term damage. 

All is not lost, though. A relatively healthy battery that's just lost some voltage through a lack of use, or exceptionally cold weather, can easily be nursed back to full health. And even an older battery can be recovered to some extent, and live to fight another day. 

But take any of the above faults as a warning that your battery needs some urgent TLC. A good, long run will help enormously, and a full charge from an external charger will work wonders. 

Click here to see our recommended battery charger and reconditioner from CTEK. 

If all else fails: How to save money on a new battery

If your battery really has given up the ghost, the best way to replace it, cheaply, is to use the price-matching service on offer at Halfords.  

If you see a price online or in another motor factors, you can pop and see the people in your local Halfords and they'll match it for you. 

There's even a fitting service, which can be important if your battery needs coding to your car. Especially with cars that have the stop/start function, it's likely modern vehicles will need their car to be linked up to a computer to "tell" the car it's got a new battery. 

This can be a pricey service at a garage, and very expensive at a dealership, which is why it’s worth pricing up the Halfords installation service. There’s also a membership system that will save even more money on batteries, fitting, and servicing or MOT costs, in exchange for a monthly fee.

Prices for car batteries at Halfords start at around £50, and you can book in for a free battery check to help you choose the right one and diagnose any issues with your old one. 

Fitting adds around £25 to £30 to the price for non-members, and it's an important consideration on modern cars. 

But don't forget the price match guarantee. Put it to the test. Find the battery you want on the Halfords website, shop around online for a better price, check the terms and conditions to see if it could be matched, and let Halfords know they need to knock some money off. 

And click here to find out more about the club membership options to see if you can save even more on your motoring costs.