I have a situation that I am not sure if the two batteries are having
problem or the on-dashboard voltmeter doesn't work reliably in cold
weather. After I had fully charged the batteries (that were left on
the boat in cold winter like 32-degree), the needle in the on-dashboard
voltmeter would show exactly 12-volt. But after the batteries had sat
there doing nothing for a couple hours later, it showed at something
like 11.5-volt to 11-volt. I am sure that the batteries were not
supposed to have been used because I had turned the battery switch to
OFF. I recharged it anyway. Strangely, after I had recharged the
batteries for less than a minute, the recharger would stop recharging
and indicate that the batteries were fully recharged. I checked the
batteries with a portable mult-meter, and I found that both batteries
were fully charged (with 12.99 volt).

Seem like the batteries are really fully recharged and they are good
because of these facts (1) The recharger had stopped recharging the
batteries and indicated that the batteries were fully charged. (2)
Nothing was using the batteries. (3) The mult-meter also said that the
batteries were fully charged.

I am wondering may be the on-dashboard voltmeter doesn't work that well
in cold weather considering the fact that the on-dashboard is being
left in the cold for a long time. The multmeter still worked well when
I used it in the boat because I brought it out from room temperature,
and it was still warm when I used it to check the batteries.

Is my understanding correct? If my understanding is correct, I will
have to stop using the on-dashboard voltmeter to check the batteries
during winter, and I should use a multmeter instead. If my
understanding is not correct, does this mean that the on-dashboard
voltmeter is no good and it should be replaced?

Thanks for any info in advance.

Jay Chan