1976 Honda 750CB battery not holding charge.

[CB750Newbie]

I’ve a new Shorai lithium battery in the bike, however, after a few miles the bike shuts off mid-ride. Used the voltmeter to check battery with the bike running. The initial reading was 13.5v, once I started the bike it dropped to 12.9v and with every passing minute it dropped 0.1v. The battery is not being charged. What should be my next troubleshooting steps please!

 

[Raggaren]

I’ve a new Shorai lithium battery in the bike, however, after a few miles the bike shuts off mid-ride. Used the voltmeter to check battery with the bike running. The initial reading was 13.5v, once I started the bike it dropped to 12.9v and with every passing minute it dropped 0.1v. The battery is not being charged. What should be my next troubleshooting

Copied from google.
CB750 charging issues.
typically stem from corroded electrical connectors, a failed rectifier, or a weak field coil/rotor. Begin troubleshooting by cleaning all connections, particularly behind the sprocket cover, checking the battery voltage (should be $\sim$12.6V+), and verifying the rectifier's output.
Key Troubleshooting & Fixes

• Corroded Connectors: The most common issue is poor electrical connection, particularly in the wire harness connectors near the engine sprocket cover. Clean all connections thoroughly.
• Rectifier/Regulator: If the battery isn't charging, the stock rectifier often fails. A modern, upgraded 5-lead rectifier/regulator combo is a common, reliable replacement.
• Field Coil & Rotor: The rotor magnets can weaken with age. Test for magnetic strength; if weak, the rotor must be replaced. Also, check the field coil ground, which often fails.
• Stator: Check the three yellow wires from the stator for AC output, and ensure there is no continuity between the stator wires and ground.
• Battery/Wiring: Ensure the battery ground wire is securely attached to a clean, unpainted part of the frame.

Testing Tips

1. Check Battery Voltage:A healthy battery should be at
   
   
   
   12.6V
   or higher at rest.
2. Test Charging Voltage:With the engine running at about
   
   
   
   2500−3000RPM
   , the voltage at the battery terminals should rise, usually between
   
   
   
   13.5V
   and
   
   
   
   14.5V
   .
3. Inspect Wiring: Look for burnt wires or corroded connectors, especially in the harness under the seat and behind the engine covers