I will never trust them if that is one of their business models. They can tell me whatever they want; I would have to believe them. They will likely tell me, "the battery is dead," then they sell me a new one and keep the old one (which is maybe not too dead), which sounds like a good deal. At least for them.... Most shops will test for free as it is a marketing model to selling you your replacement battery. ...
Anyhow. I appreciate your advice, and I would try to do the battery test described following the link, but there is no way to guarantee the temperature, and the time the test will take is a problem as well. I am three hours away from the boat and otherwise have a normal work life like every mere mortal.
Nope, it wasn't murder. It was neglect, and the batteries are not dead yet. I do actually have an excuse. Due to COVID, I was under a travel restriction from my employer for most of the winter. The boat is in another state, and believe me, we had other worries than boat batteries during this time.You murdered the batteries. Get new ones. Good luck.
Anyhow, back to the topic.
The batteries were charged the entire night. I disconnected the charger and measured both house batteries. Both showed above 13 Volt (13.3 and 13.6).
Then I waited about 30 min. After 30 min both batteries were above 12.7 V.
While I had the multimeter on the batteries, I asked my wife to start some electrical loads. She opened the faucet in the galley and head, which caused the water pump to start, then the pump for the shower sump, and finally the bilge pump. The whole time I was with the multimeter on the battery, and the voltage did not fell under 12.6 V. Maybe not enough load? Not enough time? But would a dead battery show the same behavior?
Shouldn't that be enough to start both the fridge and the freezer?
More questions than answers, and yes, this "test" might not be worth anything.
BTW. During the whole thing, the control panel showed the main battery voltage at around 11.5 Volt. So about 1 V below the measurement at the battery directly.
Thereafter, I worked my way towards the connectors of the freezer and the fridge. In my boat, both compressors are under the stove, where is kinda limited access.
I disconnected the power cables to the Freezer and measured the voltage. It was 11.4 V, pretty close to what the control panel was showing and more than 1V below the measurement at the batteries directly. From what I have read, it's unlikely that the fridge will start with that voltage.
The power connectors to the Freezer were without corrosion.
I was running out of time because we had to leave for home, so I only briefly turned my attention to the Fridge connectors. They are a bit difficult to reach and see, and I could not easily disconnect them. So I left them in place and did not do a measurement—this time.
I am not sure what to make from all of this.
Why does the panel did not show the battery voltage I can measure direct at the battery?
Why does the Freezer power cable voltage is only 11.4V when the battery has 12.6V at least?
Why does the battery voltage on the panel slowly creep up to about 12.5 V after all electrical loads are disconnected than I can start the Fridge?
I should have measured what voltage is at the Freezer when the panel shows 12.5V. Unfortunately, I did not.
The panel definitely shows nonsense numbers for the starter battery. Since I have the boat, I have not seen the starter battery voltage over 7V. Multiple measurements at the starter battery directly have always shown healthy numbers above 12.6V. But I have a 12V starter pack, just in case.
To ensure that there isn't a problem with the fridge or the freezer, even though unlikely that they will fail simultaneously, I will make a cable that I can connect to a 12 V power source and then connect to the power of the freezer or fridge. If they start with that, the problem is likely not within these units.
Based on the above, how likely is it that the batteries are the problem?
Not sure what to check next. I am pretty sure that there is a problem at the level of the panel. The panel was exchanged at least once. But does that have anything to do with the rest?