[EricK1300GTSE]

Reading the above it seems your alternator diodes are Kaput, or youve lost a phase inside the wiring of the thing. You should be seeing ~14.3-14.6v at the battery at about 3000rpm, 12.4v at rest. Seeing a continuous 12v regardless of rpm means your alternator isn't charging the battery.

These bikes are canbus and relatively sensitive to correct voltages, so if not enough, it will shut down to protect itself (ECU etc).

I think the battery might still be good enough, but needs to be tested on a carbon pile or quality battery tester. A lithium with in built bms will also protect itself by simply switching off if they get drawn down too low (e.g. below bms min voltage set point) if new, might be worth having it tested.

Dont just drop a new battery into it, as defective alternators have been known to drag brand new batteries down to failure really fast (cars and bikes).

An auto electrician would be able to confirm a failed alternator. Replacement diodes or alternator rewinds are possible. Also check all the earth connections.

Last point, remove the alternator and starter motor and clean them out with compressed air, carbon dust etc. can cause trackinh and spurious voltages. With the starter motor, you need to remove the outer cover to expose the windings, and add a bit of bearing grease to its bearings.

Best of luck mate

 

[EricK1300GTSE]

With a new battery installed, bike starts up fine at around 12.8 volts. The voltage never changes from the time I start the bike and throughout revs. I pulled the negative lead off the battery and the bike died right away.

Makes sense as the battery has enough grunt to spin the motor over. With no alternator generating power to run the system, it will stop as soon as you disconnect the negative lead, basically your 'test' to confirm its NOT the battery.

 

[EricK1300GTSE]

Alternator functions the same as a car's alternator. Similar size engines in some small cars.

An auto electrician can test the diode and check for continuity (resistance) in the wiring. If you have a multimeter, you can check if the wiring has a fault by measuring resistance between each phase and ground. Infinite resistance (Ohms) in any phase indicates a broken wire, as there should be some resistance. I'm not sure how to check diode function, hence the suggestion to take it to an auto electrician.

Get the battery checked as well as suggested.

 

[EricK1300GTSE]

To my understanding, you should not be seeing any continuity (resistance) between windings. From each winding to ground should also be infinite or open circuit,, to my knowledge, current flows to the negative terminal not to ground.

Seems to me the alternator is the issue.