Now you know the propper way to do it, I'll tell you my way
I have solar panels
direct into the batteries so it no use using the volt meter during the day... (unless...see below)
At night after the sun has gone I should have 12.7 volts with the Auto Pilot on and the chart plotter at low level scrren brightness.
At 12.2 (i.e. not 12.3 flicking to 12.2) I am hoping sunrise will be very shortly. If it isn't I will recharge with the engine
Because I know this from months of experience IF I start getting lower readings then I must determain why: Its not charging correctly; the batteries arn't holding the charge as they used to; or I have an electrical
In the last few weeks I have been at anchor
and running a fair bit on firigge and computer. The batteries suprised me the other day when they were VERY low. 11.8!!!
I thought the batteris must have been fired!
But I looked at the latitude: 44 north, the days are getting shorter, a bit of thick cloud about and using more elctricity than normal.
So it wasn't the batteries.
I take a volt meter reading several times per day and if you do the same thing you will quickly see what is 'normal' and what is not.
During the day on solar
I have between 13.1 and 14.6 volts. It the batteries are flat or something is very wrong the voltmeter will show 12.2 or whatever...
Love thy Volt Meter!