Yeah, it seems like it's charging fine. After a ride, leaving the voltmeter on, have you checked it after a while to see if something is draining your battery down? You could have a wire shorting against the frame somewhere or something draining your battery after it's shut off.
Edit: Here's a good troubleshooting method BPG posted up a while back if you think you're battery is getting drained.
Connect everything. Put a voltmeter on the battery. Note the rate at which the battery is losing voltage. Start pulling fuses one by one and not which fuse stops the battery from losing voltage. Start tracing that system thoroughly....