20mph queues on the A23 and charging systems under strain
Streatham's traffic has a lot to do with how its cars wear. The high road and Streatham Hill are 20mph red routes with buses stopping every few hundred yards, and the Streatham Wells low traffic trial pushed queues back onto the A23 for months before it was suspended. Roads like Leigham Court Road carry through traffic that stops and starts. For an alternator, all this means long periods at idle when output is lowest, often with the heater, lights and air conditioning running together.
In Streatham Vale and the terraced streets off the high road, many cars are parked on-street and used for short local trips, a run to Streatham Ice and Leisure Centre or past the Streatham Hill Theatre and back. That's not enough to recharge a battery after a cold start, and a weakening alternator makes the gap wider every week. Private-hire drivers working the A23 see the opposite problem: huge hours at low speed that wear out bearings, brushes and pulleys. Heat doesn't help either, as an alternator relies on airflow that it barely gets at 20mph.
Both cases need a proper test, not a guess. We check the battery's condition, the alternator's output at idle and under load, and any charging or battery management codes the car has stored. On newer cars with smart charging we take into account that the voltage is meant to vary. You get a written quote before anything is replaced, and we fit OE-specification alternators with a new auxiliary belt, checking the tensioner at the same time.
The route is Mitcham Lane and Streatham Road to Figges Marsh, then London Road through Mitcham to the Cricket Green, Cranmer Road and Carshalton Road into Hackbridge, about 5.5 miles. That's a long drive on a failing alternator, so we'd usually suggest collection if the light is already on. The repair comes with our 3-month workmanship warranty.