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Starter battery and starting system

The starter battery is the part that most often leaves you stranded, almost always on a cold morning. On cars with stop-start it is no longer a simple consumable either: they use AGM or EFB batteries, and many cars need the new battery registered with the energy management system. Without that, it is charged incorrectly and lasts markedly less long.

What it covers

  • Testing the battery under load, not just measuring resting voltage
  • Checking the alternator's charging voltage
  • Measuring parasitic draw if the battery goes flat overnight
  • Registering the new battery in the control unit where the car requires it
  • Cleaning terminals and earth connections

What tells you it is due

  • The starter turns noticeably more slowly in the morning
  • Stop-start no longer works — often the very first sign
  • After a few days standing, the engine will not start
  • The lights dim markedly while cranking

Worth knowing

If stop-start quietly stops working for no obvious reason, that is not a fault in the system: the energy management disables it as soon as the battery can no longer hold state reliably. It is the earliest warning the car gives — months before the engine actually refuses to start.

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