What is an Alternator / Stator?
The on-board generator that keeps the battery topped up while the engine runs.
Simplified animation — not to scale.
In plain English
Spinning with the engine, the stator generates alternating current which is then converted to the DC voltage the bike's electrics and battery actually need.
“A tiny power station bolted to the engine, permanently topping up the battery so it never runs down on its own.”
How it works
Magnets on the crankshaft or a flywheel spin past fixed coils in the stator, inducing an electrical current. That current passes through the regulator/rectifier before reaching the battery and electrics. A failing stator charges weakly or not at all, slowly draining the battery even while riding.
Signs of trouble
- ⚠Battery warning light staying lit while riding
- ⚠Dimming headlight at idle
- ⚠Battery repeatedly going flat despite regular use
- ⚠Burning smell from the alternator cover
£150–£600
Always get a written quote. Prices vary by bike, region, and parts brand.