Many electric motorcycles and scooters have a small 12 V battery as well as the big traction pack. It is often under the seat or behind a side panel. Some bikes have no separate 12 V battery and take their low-voltage power straight from the DC-DC converter.
What it does
The 12 V battery powers the dashboard, lights, horn, key switch and control electronics. It also "wakes up" the system so the main contactor can close and the bike can go to ready. While the bike is on, the DC-DC converter recharges it from the traction pack. If the 12 V battery is flat, the bike can seem completely dead even with a full traction pack.
Signs it is worn or failing
- Dashboard dark, nothing happens: Dashboard is dark.
- Small battery flat after parking: Small 12 V battery is flat.
- Dash on but no ready, clicking: Will not go to ready.
- Lights dim or warnings flicker.
When to replace it
Test it first; a flat battery may only need charging and the real fault may be the DC-DC converter or a drain. Replace if it will not hold charge, is swollen or leaking.
What to match when buying
- The battery code, size and terminal position on the old battery or in the manual.
- Chemistry: lead-acid (AGM) and lithium 12 V batteries need different chargers. Fit the type the maker specifies.
- Buy fresh stock from a known brand; check the date code.
Fitting notes
- Switch the bike off. Disconnect negative first and reconnect it last.
- Do not jump-start from a car with the car engine running unless the maker allows it.
- See Check the 12 V auxiliary system, and for charging and testing the battery Test and charge a 12 V battery.