A quarter of UK cars—more than 8.6 million vehicles—may be at risk of breakdown due to weak 12-volt batteries, according to new analysis by automotive diagnostics firm Carly. Out of 34.49 million licensed cars, Carly’s review of over 550,000 vehicles from January 2025 to January 2026 found that approximately 25% have batteries in poor condition, with the worst-affected brands seeing rates above 40%.
Unlike major mechanical faults, 12-volt battery decline often develops unnoticed, leaving motorists vulnerable to sudden non-starts, roadside breakdowns, and unexpected repair bills. The 12-volt battery powers essential electronics such as central locking, alarms, and keyless entry. Its failure can disrupt security systems and even personal safety, especially if a breakdown occurs on a high-speed road or in remote areas.
Older vehicles, short-trip vehicles, cars with start-stop systems, and models laden with electronics are particularly susceptible. Extended periods of parking and cold weather can also accelerate battery decline, with many drivers missing early warning signs. Subtle symptoms include hesitant engine starts, dimming headlights during ignition, deactivated start-stop systems, unexplained warning lights, and briefly heavy power steering after startup.
Emma Brown, UK Growth Manager at Carly, noted: “Battery degradation develops gradually, so it’s easy for drivers to miss the warning signs until the vehicle suddenly fails to start. Early diagnostics and battery health checks are vital to prevent disruptive breakdowns and mounting repair costs.”
While replacing a 12-volt battery typically costs £150–£330, issues with the starting or charging systems can push repairs to £800 or more. Carly’s OBD2 Scanner and App aim to help drivers detect battery problems early, understand fault codes, and estimate repairs, potentially saving motorists from costly interruptions.
You can read and view more about how Carly’s OBD solution can help drivers here.
