It sounds like whatever means you are using to charge the battery while it's running has some issue. 14 volts is pretty good for a charging system at work, 12.3 is just slightly low for a battery that is assumed to be fully charged at rest.

1957 Chevrolet 5700 LCF 283 SM420 2 speed rear, 1955 IH 300U T/A, 1978 Corvette 350 auto, 1978 Yamaha DT175, 1999 Harley Davidson Softail Fat Boy