Do we have a Battery or a Fridge issue?

Jun 24, 2019
Beneteau Oceanis 40 Rock Hall
... Most shops will test for free as it is a marketing model to selling you your replacement battery. ...
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.

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.

You murdered the batteries. Get new ones. Good luck.
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.

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?
May 17, 2004
Beneteau Oceanis 37 LE Havre de Grace
Based on your measurements I’d say the batteries aren’t necessarily in the clear, but they also aren’t the primary source of your problems. Over 1V of drop from batteries to panel is definitely too much. The fridge/freezer get their power from the panel so it makes sense that their voltage would be close. The rebounding of panel voltage after you turn off the load is because once the load is off there’s no current to cause the voltage drop. If the change isn’t instant I’m guessing it’s just an electronic meter in the panel using some degrading average to smooth its display value.

My recommendation would be to keep tracing wires, both positive and negative, between the panel and battery terminals, to find where the primary source of the drop is. Do the testing with as many panel driven loads as you can (pumps, lights, electronics, etc). You can also measure the voltage right across some connections, like the sides of any fuse blocks, to see if there’s a drop in them.
Nov 21, 2012
Yamaha 33 Port Ludlow, WA
Based on the OP's descriptions he has a bad connection somewhere causing excessive voltage drop. It is now an issue because his batteries are dying.
May 24, 2004
CC 30 South Florida
Don't know how many batteries does your house bank has, but if it is less than 3 take them out and take to auto parts retailer for a free check up. The one I have used is a local Discount Auto and they have a computer tester that besides checking the voltage it conducts a load test and spits out a piece of paper indicating the results and the approximate percentage of capacity left. If the battery is dead or has a bad cell it will tell you to replace it. You cannot fix or diagnose any other problems until you have healthy batteries. The fact that you have been able to start the appliances after charging the batteries tells me the batteries are not holding charge, at least one of them is surely dead.


Jan 29, 2018
Beneteau 411 Branford
Some of the freezer compressor modules have low voltage protection and shut off automatically so they don't run a battery to zero. You can check the manual on your compressor module to see if this is the fact.
Jan 18, 2016
Catalina 387 Dana Point
Disagree, if the OP can measure a > 1v voltage drop between the batteries and the fridge or panel, there's another problem and it's a bad connection/corroded wire/etc..

(Not that the batteries haven't been murdered too)

Get a long wire and hook it between (-) on a multimeter and the negative terminal of the battery. With load ON (the fridge is running), measure the positive side of the battery. Then just follow the wiring. The positive side of the battery switch, the feed to the panel, the breaker for the fridge, the fridge itself. Wherever the voltage has a big drop, there's where the problem is. I would do all of the above with the charger feeding power so it's all independent of the batteries.

If the + side never shows a drop, do the same for the - side. Fix the voltage drop problem.

THEN - find out if your batteries are toast (and they very well may be)
May 24, 2004
CC 30 South Florida
Appliances especially more than one do not simultaneously die from one day to the next. Last used the boat was fine, unlikely the wiring and connectors got fouled up with the boat resting on the hard for 5 months. Now 5 months is a significant amount of time for batteries left unattended to foul up. The history points to the batteries, the symptoms described point to bad batteries with no capacity, I would say it is likely the batteries. All the components could be tested but the process may require time and effort and tools which may be more taxing than a simple process of elimination. All you need to determine if it is the batteries is one single 12V battery that is known to be good. Take it out of the car if you need to. Connect it for a few minutes to the appliances/ charger circuit and turn them on. No need to worry about damaging a starter battery in a short test. The problem will not get solved until someone gets their hands dirty.
  • Helpful
Likes: jssailem
Jul 23, 2009
Beneteau 31 Oceanis Grand Lake, Oklahoma
Check for voltage drop across the battery switch. Both of my Beneteaus had a significant drop at the main switch. One due to dirty contacts and the other I attributed to the use of loctite on the cable connection.
Jan 9, 2017
Beneteau 40 Oriental NC
My B40 2008 has the same problem! While anchoring on battery power overnight and the battery level drops to the low 11v range and we operate the electric head or anything which draws a momentary SURGE from the batteries the refrigerator drops out at the Danfoss defalt low voltage setting 10.4V but the freezer locker continues to run. The worst part of this problem is the Danfoss compressor won‘t restart until the battery voltage reaches 11.7V, in our case we have an onboard generator so it’s not the end of the world.
Below is a link to the Danfoss info sheet for our compressor.
I have considered running + / - wiring from the compressors directly to the batteries to avoid the surge through the VDO panel which always reads .5V lower than the Magnum monitor for the charger/inverter.
Anyone with experience?
Jun 15, 2012
Hunter 50 AC St. Petersburg
I'll bet you need a new Secop 101N0500 controller. It's an electronic device which converts 12VDC to AC to run the compressor. They cost around 90 bucks and your going to need one sooner or later.
Jun 26, 2021
Beneteau 43 Dalhousie
Thank you. Just wondering if you have a link where to purchase this controller?
And, where is it typically located? Close to the compressors or?

I'll bet you need a new Secop 101N0500 controller. It's an electronic device which converts 12VDC to AC to run the compressor. They cost around 90 bucks and your going to need one sooner or later.