My experience is with highway vehicles, not boats, but your description
sounds like a low level of corrosion in the wiring to me.

I'm guessing that there is a layer of oxidation in several different
connections that's too thin to see, but thick enough to create a slight
resistance and screw up the voltages.

I suggest that you clean ALL of your battery posts and clamps until they
shine, whether they need it or not. Then go to the other end of the
cables and clean them up where they mount to the electrical system.

I'm thinking that if you go through a normal cycle of use after all of
the connections are shiny and tight, the voltages will look better at the
end of a charge.

On Sun, 18 Dec 2016 10:43:57 -0500, Flying Pig wrote:



We've been fully charging about every 2-3 days of late, due to work
we've been doing which requires the Honda, and yesterday I fully charged
(one hour at 14.1V or better) and equalized (2 hours at 15.2V or
better), and immediately read the batteries with a
temperature-compensated hydrometer and also our voltmeter, at the end,
while still charging, the individual battery voltages (ya, I know - they
weren't disconnected).

The 4 had divergent readings at the end of the equalization cycle: 8.0,
7.3, 7.33 and 6.68 volts. The banks/pairs are 1/4 and 2/3, and,
cumulatively, the banks had the same readings, but with very different
single readings. I suppose that could be laid to the fact that I
couldn't effectively disconnect them, but it's still pretty weird...

Temperatures were very different between banks one and two (read down
each water-fill hole; I've averaged the 3 readings per battery)
immediately after equalization:75, 98, 100, 73F - from which I
gather/intuit that bank one (1/4) got much less amperage, somehow, or
there was some problem in bank 2.