A weak battery is responsible for most starting problems and electrical faults reported by owners. Think of an ABS warning light coming on, systems cutting out, or vague messages on the dashboard. Regular maintenance of the battery and the associated wiring prevents many of these problems. Owners of, for example, the Dacia Sandero often recognise this: the car starts reluctantly or shows unexpected fault messages. Curious how to spot it and deal with it yourself? Read on quickly.
Why is the battery not charging properly?
In many models, a poorly functioning battery is the cause of starting difficulties in around 90 per cent of cases. The battery not only supplies energy to start the engine, but also supports electrical accessories when the alternator is not delivering enough power. On average, a battery lasts 5 years. An ageing battery can no longer cope with the engine’s demands. This becomes particularly noticeable in cold weather.
Typical signs of a weak battery are:
- The starter motor does not turn at all or only weakly.
- Dashboard warning lights are dimmer than usual.
- Messages such as “battery discharged” or a breakdown emergency situation appear on the screen.
Electrical faults: causes and fixes
Not every fault is caused directly by the battery itself. Other electrical components can also cause similar complaints. Users regularly report messages such as “battery charging priority” or “battery is charging”. The real cause is often a faulty 12V battery current sensor, the component that measures the battery’s current and passes this information on to the battery management system.
Other common causes of electrical faults are:
- Excessive charging voltage from the alternator, causing the battery to overcharge and become damaged.
- A software fault in the drivetrain, causing the engine not to stop or the start button not to respond.
- Dim lights or isolated faults, which may indicate problems with the battery management system.
If you want to tackle these faults, follow these steps:
- Check the battery terminals for corrosion and tighten them properly. Loose or oxidised terminals are a common, easy-to-fix cause of faults.
- Carry out a parasitic current draw test. If the battery drains without the car being used, a short circuit in the system may be to blame.
- Have the battery and alternator tested by a specialist. This will tell you for certain whether the battery is weak, or whether the alternator is supplying insufficient voltage while driving.
- If messages persist, read the fault codes from the battery management system and drivetrain modules. This distinguishes a battery problem from a software problem.
How do you test the battery yourself?
If you are unsure whether the battery is the cause of starting problems or faults, first check the basics. Make sure the battery terminals are clean and securely fastened. Use a battery brush to remove oxidation from the battery posts and connectors. This immediately improves voltage transfer and is often enough to solve minor starting problems.
If the car still starts reluctantly, have the battery professionally tested at a garage or parts shop. A flat or weak battery can prevent the whole vehicle from starting, even if other systems are functioning perfectly. If the battery is working properly, but the voltage does not hold up while driving, the problem is often with the alternator.
Owners’ experiences with battery problems
On online forums, users regularly report that replacing both the battery and the battery cables completely solves the problems. The cause is often blamed on the battery, when in reality the issue lies in the wiring or the earthing. Starting problems in cold weather are also common: the battery can no longer start the engine then. Replacing an ageing battery with a newer, more powerful variant solves this in many cases.
Some owners also warn against replacing the battery too hastily. If the symptoms point to voltage problems while driving, check the alternator and wiring first before buying a new battery.
Maintenance and costs at a glance
A car battery does not last forever. Expect an average lifespan of 5 years, after which replacement is recommended to prevent starting problems. The cost of replacing a battery is usually around €164 all in, including a parts warranty, labour and software coding.
When dealing with a faulty battery or starter motor, keep the following in mind:
- Never push-start the car if the steering column is locked.
- If you break down, you may be able to connect another battery, or call professional roadside assistance.
- For faults such as an engine that will not stop, briefly pressing the start button may provide a temporary solution, but a proper diagnosis remains necessary.
Find out more about car problems and maintenance
A weak battery and electrical faults can often be recognised and fixed quickly with the right approach. Checking the battery terminals, battery and alternator systematically makes the real cause clear. On Carnews you will find many more articles about car problems, maintenance tips and experiences from other motoring enthusiasts. Find out on the website which faults occur more often in your car model and how you can tackle them yourself.
Frequently asked questions
Common early signs of a weak battery are slow or hesitant starting, dimming headlights or interior lights, unexplained electrical faults and warning messages such as “check battery/accumulator” on the dashboard. You can make an initial diagnosis yourself by paying attention to how freely the engine turns over when starting and whether the lights become noticeably brighter once the engine is running (the alternator is then charging). Also check whether the battery terminals are clean and firmly secured, and remove any corrosion. With a simple multimeter you can measure the voltage: around 12.6 V with the engine off and about 14 V with the engine running usually indicates a healthy battery and charging system.
Many short journeys, lots of idling and regularly deep discharging the battery (leaving the car parked for a long time with electrical consumers switched on) shorten the battery’s life; plan longer journeys from time to time and avoid unnecessary idling. Heavy aftermarket consumers such as powerful sound systems, extra lighting or cool boxes connected directly to the battery can overload it; have them professionally fitted with fuses and preferably via an ignition-switched live. Permanent accessories that draw power continuously (dashcams, trackers, alarm systems) can cause parasitic drain; choose energy-efficient equipment and have the parasitic consumption measured. Also make sure the battery terminals are clean and securely fastened, and replace an ageing battery in good time to prevent overloading due to poor capacity.
Besides the battery, the alternator, the battery cables/earth points and the 12V battery current sensor are the most common causes of faults. Look out early for symptoms such as dimming or flickering lights, strange warning messages (“battery charging priority”) and voltage differences while driving. Regularly check and clean the battery terminals and earth connections, have the alternator charging voltage measured and read out fault codes if messages persist. This way you can spot wear or poor connections before they cause a breakdown.
Measure the alternator’s charging voltage with a multimeter on the battery terminals: with the engine off you should see around 12.4–12.8 V, and at idle with consumers on about 13.8–14.5 V; if you are well below or above that, there is a charging problem. To measure leakage current, switch the car completely off, remove the key/card, close all doors (lock in the “closed” position) and wait a few minutes for all modules to go to sleep. Then disconnect the battery’s negative terminal and set your multimeter to the mA setting in series between the battery terminal and cable; a quiescent current roughly above 30–50 mA (depending on the car) indicates a parasitic drain. Then remove the fuses one by one while watching the multimeter: the fuse when the current suddenly drops is usually where the leak is coming from.
Essential tools include a digital multimeter, good lighting, insulated hand tools (screwdrivers, a set of pliers), a battery brush and contact spray, plus perhaps a fuse puller and spare fuses. Essential techniques are: systematically checking fuses and earth connections, visually inspecting wiring and connectors, and measuring voltage across the battery, fuses and suspect circuits. Always work with the ignition off and, if possible, the battery’s negative terminal disconnected when carrying out dismantling work, and avoid short circuits by never allowing uninsulated metal to touch the positive and negative terminals at the same time. If you are in any doubt about airbag, ABS or high-voltage parts (hybrid/EV), do not open the car yourself, but seek professional help.
