I don't know your machine but I suspect you have an alternator instead of a dynamo.
A 12-vdc battery is rated nominal at 12-volts and would be expected to 'see' approximately 13.8-volts while engine running and charging at high-idle.
Use a voltmeter (inexpensive needle type if you're just learning how to use one) and 'look' at your voltage across the battery terminals.
I'd also look for a fuse in the system somewhere. Or a wiring harness fault.
On Kubota tractors (virtually any machine) the corrosion around the battery negative cable connection to the chassis ground point is often a problem. Clean well and reinstall with a conductive thread sealant like Kopr-Kote.
Please post back your experiences so we may all learn.
