Batteries charging at different rates

[TADTOOMUCH]

My port engine Gage shows that the charging rate is 13.5 volts and the starboard engine only charges at 12 volts. Both batteries are same make and age and swapping Sides has no effect. Both have full charge. Any suggestions why this is?

[prowlersfish]

At 12 volts you are not charging the battery . A fully charge battery will be at 12.6 volts with no static charge , you need a minimum of 13.5 to charge a battery I like to see 14-14.5 volts charging

Check your volt meters and use a DVOM to check your charging system.
Make sure your belts are tight.

[randyp]

....and make sure you don't have just one battery isolated with a switch.

[TADTOOMUCH]

I think I may have found the problem. I had a loose connection at the battery. I also noted a minor voltage difference now with port charging at 14.0volts at first and dropping to 13.5 with the stb charging at 14.9 volts and then dropping to 14.3 after a while. I did verify the house lights are on stb battery so that's maybe why a higher charge initially but I do have a shore power charger when docked so they both should be fully charged most of the time.