Low Voltage on 135 HP OPTIs

[Angelo321]

The voltage on my twin 135 HP OPTIs do not go above 12 volts while on plane. At trolling speed they come up ~ 12 volts. This a new issue that recently started. I have a 3 battery system, the battery for each motor are new purchased and installed in July 2017. The third battery is about 2 years old. I typically run with all 3 batteries electrically tied together. The motors are 2003 vintage and run good. I inadvertantly left the left key switch on for several days. I was wondering if this could have caused a problem in the electrical system. Any thoughts on what can be wrong. Angelo

 

[Docksidemarineservices]

Check the output of the Alternator directly at the alternator.

 

[Angelo321]

Thank you check and post. Both motors are behaving with low voltage indication.