Home mechanic (basic tools) ยท Time: 20 to 40 min (estimate) (estimate)
Many electric motorcycles have a small low-voltage system that runs the lights, horn, dashboard and the computers that switch on the big battery. Some have a small 12 V auxiliary battery; others take 12 V straight from the traction battery through a DC-DC converter (a box that steps the high voltage down to 12 V). If this low-voltage side fails, the bike can look completely dead even with a full traction battery, because the computers and the main contactor (the heavy switch that connects the big battery) cannot wake up.
Safety
- Work only on the 12 V side. Do not open the traction battery, the DC-DC converter or the controller. See Make an electric motorcycle safe to work on.
- Turn the bike off and unplug the charger before you touch any 12 V wiring.
- A 12 V lithium battery needs a charger made for lithium. A lead-acid charger can damage it.
- Never jump-start an electric motorcycle from a running car or another bike unless the manufacturer's manual says how.
You need
- Multimeter set to DC volts.
- The owner's manual, to find where the 12 V battery and fuses are, and whether your model has a 12 V battery at all.
- A charger that matches the battery type (lead-acid/AGM or lithium).
Steps
- Find out from the manual whether your bike has a 12 V battery. If it does not, skip to step 7.
- Remove the seat or cover and find the 12 V battery. Look for loose, corroded or green terminals.
- With the bike off, measure across the 12 V battery terminals. Write down the reading. Compare it with the value in your bike's manual; for a lead-acid battery, also see Test and charge a 12 V battery.
- If the terminals are dirty or loose, clean and tighten them: Clean and tighten battery terminals.
- If the reading is low, charge the battery with the right charger, then try to power the bike on.
- If the bike wakes up, measure the 12 V battery again with the bike switched on and in ready mode. On many bikes the reading should rise because the DC-DC converter is now charging it. If it does not rise, the converter or its fuse may be faulty: this is workshop work.
- Check the low-voltage fuses: Check fuses and relays. Replace a blown fuse only with the same rating. If it blows again, stop and see Fuse keeps blowing.
- Check the earth (ground) wires near the battery and frame: Clean and tighten earth connections.
- If the 12 V battery goes flat again after a few days parked, look for a drain: Find what is draining the battery. Alarms, GPS trackers and fleet telematics units can drain a small battery.
Check your work
- The dashboard lights up at key on and the bike goes to ready.
- The 12 V reading rises when the bike is on (where the manual says it should).
- The battery holds its charge after the bike is parked for a few days.
If it did not fix the problem
- 12 V is good but the dash stays dark: Dashboard is dark and the bike seems dead.
- Dash is on but no ready: Dashboard is on but the bike will not go to ready.
- 12 V battery keeps going flat with no drain found: the DC-DC converter needs a workshop check.
- Before long parking, see Store an electric motorcycle.