More than 2,8-million cars on South African roads could be running on borrowed time with weakening batteries. With approximately 11,2-million licensed vehicles in the country, fresh analysis from the UK suggests one in four vehicles could be driving around with a 12-volt battery in poor condition – leaving owners open to unexpected non-start issues, security glitches and avoidable repair costs.
The findings from UK automotive diagnostics company Carly – based on data from more than 550 000 vehicles in that country analysed between January 2025 and January 2026 – reveal across most car brands, roughly 25% of vehicles could be operating with a 12-volt battery on its way out.
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In the worst-affected cases, that figure climbs to more than 40% – meaning two in five cars could be at risk. Unlike major mechanical failures, 12-volt battery decline happens slowly, often giving little to no warning. For many drivers, the first sign of trouble is a car that simply won't start – usually at the most inconvenient moment. Carly's data shows failing 12-volt batteries remain one of the leading causes of roadside breakdowns across the country's vehicle parc – and the same could be true here in SA.
In modern vehicles, the impact of a weakened 12-volt battery extends beyond just inconvenience. Low battery voltage can affect vehicle reliability, compromise personal safety and disrupt security systems – particularly if a breakdown happens on highways, at night or in remote areas like the N1 outside Beaufort West or along coastal routes far from the nearest town.
As the 12-volt battery powers essential 'body' electronics such as central locking, alarms and keyless entry, degradation can also cause locking systems to behave unpredictably or leave vehicles temporarily unresponsive.
Although battery degradation can affect vehicles of all fuel types and ages, Carly's data suggests the risk increases for older vehicles, cars used mainly for short urban trips, vehicles equipped with start-stop systems and models with high electrical demand from infotainment and driver assistance features.
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Vehicles left parked for extended periods can also be more vulnerable, particularly during colder conditions in places like Gauteng during winter, increasing the likelihood that early symptoms go unnoticed before a failure occurs.
Commenting on the findings, Emma Brown, UK Growth Manager, said: "Because battery degradation develops gradually, it's easy for drivers to miss the warning signs until the vehicle suddenly fails to start. In modern cars, a weak 12-volt battery can affect far more than just starting the engine, which is why early diagnostics and better visibility of battery health are so important. Identifying issues sooner can help drivers avoid more disruptive failures, breakdowns and the knock-on repair costs that often follow."
Carly's diagnostics show many drivers may experience subtle warning signs long before a breakdown occurs. These commonly include sluggish or hesitant engine starts, headlights briefly dimming during ignition, start-stop systems disabling themselves without a clear fault message, intermittent warning lights after a vehicle has been left unused and power steering feeling briefly heavy immediately after start-up. When these signs are ignored, the likelihood of a sudden and disruptive failure increases significantly.
While the immediate cost of addressing a battery issue is often relatively modest, the financial impact can escalate quickly when degradation is left untreated. Based on local pricing benchmarks, replacing a 12-volt battery typically costs between R1 200 and R2 500, including parts and fitting.
However, if a reported 'battery issue' is actually linked to the charging or starting system, costs can rise significantly, with starter motor repairs averaging around R2 500 and alternator repairs typically ranging from R2 000 to R6 000, depending on the vehicle.
Colin Windell for Colin-on-Cars in association with
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