A loose or corroded terminal is one of the most common reasons a bike will not start. The starter needs a large current, and a dirty joint stops it even when the battery is good. This job also covers the main earth (ground) cable from the battery to the frame or engine.
Safety
- Glasses and gloves on. The white or green powder on terminals is acid salt and burns skin and eyes.
- Key OFF. Do not disconnect the battery with the ignition on (K-Light 125 manual).
- Remove the negative (−) cable first and fit it last.
- Keep baking soda water out of the battery cells.
You need
- Baking soda mixed in a cup of water.
- A small wire brush or emery paper.
- Grease or petroleum jelly for the terminals.
- New terminal bolts if the old ones are rusted or the threads are damaged.
Steps
- Key OFF. Remove the cover to reach the battery.
- Undo the negative (−) cable, then the positive (+).
- Brush baking soda water onto the corrosion. It fizzes as it neutralises the acid. Wait until it stops.
- Rinse with a little clean water and dry with a cloth.
- Brush the battery posts and the inside of each cable end until the metal is bright.
- Look at each cable: if the insulation is cracked or swollen, or green corrosion runs inside the cable, replace the cable.
- Follow the black negative cable to where it bolts to the frame or engine. Undo it, clean the contact face to bare metal, and refit it tight. See also Clean and tighten earth connections.
- Refit the positive (+) cable first, then the negative (−). Tighten so you cannot turn the cable end by hand. Do not overtighten: a cracked post means a new battery.
- Put a thin film of grease over each terminal, not on the case.
- Refit the cover.
Check your work
- Try to twist each cable end by hand: it must not move.
- Press the starter: it should crank at normal speed, with no clicking.
- If you have a meter: while a helper presses the starter, touch the probes across each joint (cable end to battery post). Any clear voltage across one joint means it is still poor. See Do a voltage drop test.
If it did not fix the problem
- Corrosion comes back fast: the battery may be overcharged or leaking. See Battery terminals are corroded.
- Still clicks or cranks slowly: Test and charge a 12 V battery, then Test the starter circuit.