The battery terminals or cable ends are covered with white, blue or green powder, or the metal looks eaten away. This is acid salt. It forms when acid vapour or liquid escapes from the battery and reacts with the metal. A thin film is common on older flooded batteries. Heavy or fast-returning corrosion points to overcharging, a leaking battery, or a missing vent tube. Corrosion adds resistance, which causes slow cranking, clicking, dim lights and faults that come and go.
Is it safe to ride?
With care. The bike may fail to start or lose power to its ECU on bumps. Clean it soon.
Quick checks first
- Wear gloves and glasses. The powder is acidic.
- Is it on the positive, the negative, or both terminals?
- Is the battery case wet, cracked or swollen?
- Flooded battery: is the vent tube fitted and clear?
- Does the starter click or crank slowly?
Diagnose it step by step
1Is the battery case swollen, cracked or leaking?
- Yes: replace the battery. See Battery is boiling, swollen or leaking.
- No: go to step 2.
2Clean the terminals and cables: Clean and tighten battery terminals. Is the metal sound underneath, and does the cable grip tightly?
- No, the cable is eaten through or green inside its insulation: replace the cable. A post that is cracked or eaten away means a new battery.
- Yes: go to step 3.
3Is the main earth cable to the engine or frame also corroded?
- Yes: Clean and tighten earth connections.
- No: go to step 4.
4Flooded battery: is the vent tube in place, unkinked and routed down and away?
- No: fit and route it correctly.
- Yes, or sealed battery: go to step 5.
5After cleaning, does the corrosion come back within weeks?
- Yes: check for overcharging. Test the charging system. K-Light 125: 14.5 ± 0.5 V at 5000 rpm. Above range: Battery overcharges and bulbs blow.
- No: grease the terminals and check them at each service.
6Has the battery been weakened by long poor contact?
- Test and charge it: Test and charge a 12 V battery.
Causes, most likely first
| Cause | How to confirm | Fix |
|---|---|---|
| Normal acid vapour on an older flooded battery | Light film, slow to return | Clean and tighten battery terminals |
| Missing or blocked vent tube | Tube missing or kinked | Fit and route the vent tube |
| Overcharging | Charging voltage above range | Test the charging system |
| Leaking or cracked battery | Wet or damaged case | Replace a 12 V battery |
Reference values (K-Light 125)
| Item | Value | PDF page |
|---|---|---|
| Charging voltage | 14.5 ± 0.5 V at 5000 rpm | 78 |