Consumer champion Which? has published research exposing a widespread 12v battery defect in Toyota and Lexus hybrid vehicles that has left occupants trapped inside their cars.
The organisation's annual car reliability survey found that certain models suffer from disproportionately high failure rates for their auxiliary batteries.
The Lexus LBX recorded a 29.2 per cent battery problem rate, while the Toyota Yaris Cross stood at 19.1 per cent, far exceeding the 5.6 per cent average across all hybrid brands.
After publishing initial findings in May, Which? received over 270 responses from affected owners, with more than three-quarters involving Toyota or Lexus vehicles, including the RX, NX, C-HR, Corolla and Yaris.
The safety implications are most alarming in vehicles fitted with electrically operated doors, which cease to function when the 12V battery dies.
Michael, from North Lancashire, told Which? that after his year-old Lexus NX's battery failed twice, occupants were left unable to exit.
Not knowing about the manual override, he smashed a window to allow air in for two adults and two dogs, resulting in him paying £278.30 for a replacement battery and new glass.
Mary Mitchell described her grandchildren becoming locked inside her Lexus LBX with the keys. "The children were panicking, and it was extremely stressful," she said. "We eventually managed to get a window open and get the children out."
James Houston, from Northamptonshire, reported six battery failures in his Lexus RX's first year. His wife became "extremely distressed, believing she was trapped inside the vehicle" after the rear door would not open normally.
Dozens of owners reported being told by dealerships that insufficient mileage was causing their battery problems. Robin, from the East Midlands, said the dealer insisted he should cover 10,000 miles annually or leave the car powered on while parked for an hour each week.
"The dealer's service department clearly had a script that they were going to stick to, no matter how daft parts of it sounded," he claimed.
Sarah was advised to drive her Yaris Cross along a dual carriageway "for nine miles and back, twice a week" to maintain charge, and spent £60 on a solar charger instead.
Department for Transport figures showed average non-commuting annual mileage is just 4,500 miles, well below the 7,000 to 10,000 miles dealers were recommending.
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Toyota responded to Which?'s concerns by explaining what owners should do if their 12V battery fails, including instructions for operating manual door overrides.
The company said it would share this information with its dealer network and confirmed that Lexus would follow suit.
"Customer safety remains our highest priority, and we recognise the importance of ensuring customers are familiar with the manual override features fitted to these vehicles," it stated.
Toyota also said it had conducted online training for dealers on battery issues and improved its diagnostic tools since May, while battery inspections are offered free of charge.
Which? has called on Toyota and Lexus to order dealers to stop blaming owners for not driving enough, provide written warnings to prospective buyers about minimum mileage requirements, and refund anyone who has paid for batteries or trickle chargers regardless of warranty status.
The consumer group is also pushing for software updates to reduce power consumption and for direct communication with every registered keeper of a vehicle fitted with electric door switches, including second-hand buyers.
Which? has suggested using DVSA records to contact all affected owners by letter, though Toyota has not yet confirmed its approach.
If the company's response remains inadequate, Which? has warned it may escalate the matter to Trading Standards and the Competition and Markets Authority on behalf of affected customers.
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