Unit Voltage display on Garmin

[JeffRad54]

I recently discovered I can display Unit Voltage on my chart plotter. Sweet.
But I'm really confused after a week long trip as to what it is really showing me.

Cruising at 1700 RPM, full sun, my Unit Voltage shows 14.4 - 14.5 volts.
What's running? Two fridges, the chart plotter, auto pilot, VHF, batter charger. I also have the Inverter running.
Going through a lock, using the bow thruster while floating, the voltage drops to 13.5 or less, depending on how much I use it, naturally.
At anchor, with the chart plotter, anchor light, and fridges running (fridges have all cold items by now), the Low Voltage Inverter alarm will go off after about 10 hours. I can start the engine and the voltage will climb. That tells me the engine alternator is also feeding the system. Good news.

Here's the odd thing. On Shore power, my Unit Voltage will go no higher than 13.5 volts.
My question is, what does Unit Voltage tell me? I know the Thruster battery is only for the Thruster and Genset Start and is separate from the House batteries (2). Why is my UV higher (14.5) underway than on Shore Power (13.5)?

Thanks,
Jeff

 

[Katmat]

That is what your alternator is putting out.

 

[knotflying]

You are reading what is happening at that specific time. When underway that is the voltage output from the alternator. On shore power it is the voltage being supplied by your charger. When anchored out it is the voltage in the battery bank that the Garmin is attached to, I believe the house bank. When on the hook you should use as little battery power as possible. Inverter should be off (on when only needed) as well as the Garmin and other items that will suck out power not required.

 

[iggy]

You are reading what is happening at that specific time. When underway that is the voltage output from the alternator. On shore power it is the voltage being supplied by your charger. When anchored out it is the voltage in the battery bank that the Garmin is attached to, I believe the house bank. When on the hook you should use as little battery power as possible. Inverter should be off (on when only needed) as well as the Garmin and other items that will suck out power not required.

Yep!

 

[JeffRad54]

You are reading what is happening at that specific time. When underway that is the voltage output from the alternator. On shore power it is the voltage being supplied by your charger. When anchored out it is the voltage in the battery bank that the Garmin is attached to, I believe the house bank. When on the hook you should use as little battery power as possible. Inverter should be off (on when only needed) as well as the Garmin and other items that will suck out power not required.

Thank you!