Battery warning light on: alternator and charging

The battery warning light (battery or amp symbol) indicates a problem with the charging circuit: usually the alternator is no longer charging (or not charging enough). Driving with this light on can lead to a flat battery within a few miles.

Common causes

Alternator faulty: regulator, brushes, diode or bearing. Accessory belt slipping, worn or broken: alternator pulley no longer turns. Wiring or connectors corroded or broken. Battery at end of life no longer holding charge (light may come on when stopped or under load).

What to do

Avoid switching off the engine unnecessarily: when stopped, lights and electronics drain the battery. Reach a garage as soon as possible. Avoid long journeys and unnecessary loads (air conditioning, full beam if possible). Have charging voltage (engine running) and alternator (regulator, belt) checked.

Order of magnitude for costs

Alternator (reconditioned or new): €300–800 and more depending on vehicle. Accessory belt: €80–250 (parts and labour). Regulator only: €80–200. My Auto Check-up helps you prepare your garage visit for a cost estimate.