Battery at Near Zero

While on the hard plugged in to shore power in the shipyard having our bottom painted a shipyard worker mistakenly unplugged us during freezing temps here in Mississippi causing the space heater and bilge heater to draw down my 1 year old AGM batteries. What are my concerns, and what is a reasonable remedy?

Ethan, sorry to read about the battery problem. I’ll address what I would expect if the batteries are toast. I’m not saying they are, that’s for someone with battery intelligence. If they are toast I think it reasonable to ask the yard for financial help with replacing batteries that are faulty, if they are.

Jim F

It is never good to totally deplete a charge on AGM batteries. The real question is how long they were depleted. I have found AGM's to be somewhat forgiving of deep discharge conditions.
The problem in charging them with digital automatic chargers to find the level of damage is that many chargers do not recognize a battery of aprox. 10.5 volts or less and throw an error code. I have found that using an "old school " charger to bring each battery back to 11.5volts or greater will allow for recognition and charging on most digital chargers.
Another option is finding battery specialist......not just some auto parts store or big box salesman......some marinas have really good electronics guys with proper gear ...some stores like Batteries Plus or Batteries and Bulbs are good sources too......
If none of those work for you....then pursue the boat yard for replacement of those batteries as previously noted...
Best of luck............

I had my house batteries totally discharged on my 2011 R29. They were the factory AGM batteries. This was quite a few years ago, but was also in freezing temperatures. I plugged in the boat and let them charge as normal and continued to use them up until changing them this past summer. When replacing them I load tested all 6 batteries and found the 4 house batteries tested replace but the starting battery and the thruster battery tested good. I still changed them all. I changed out my solar controller and monitor the batteries a lot more now and there is a noticeable difference with the new batteries but the old ones were also 9 years old with 8 years of service I now fully charge the batteries and disconnect the power cables for the winter. I had all battery switches to off when they somehow discharged.
I would take Jim’s advice and seek replacement but given the cost I am sure it will be a fight. In my case I was ok but We have a generator and solar panel and honestly do not ever really push the house batteries to their limit. As long as I can make coffee in the morning with the inverter when we are on the hook, I’m in my happy place 🙂
Good luck.

I purchased new AGM Northstar batteries last spring. On our first trip (trailering over road trip) I loaded the refrigerator up with food turned the batteries on and ran the fridge. If the fridge door stays closed we get easily a couple days of travel and the house battery manages well. On this trip I forgot to swing the latch that locks the fridge door closed. When I got to the launch ramp (6 hour trip) and got in the boat to prepare for launching. I noticed the fridge door open and some food scattered throughout the pilot house and V berth area. The fridge had been running non-stop for hours and depleted the batteries to reading 9.5 V, read from the analog gauge at the panel. I had the same thoughts as Ethan. The thruster ( luckily I didn't have my thruster to house parallel switch, that I added, turned on) and engine batteries not effected but 550.00 worth of house batteries possibly destroyed. When I launched and started the engine I immediately tuned the engine to house parallel switch on to excite the house batteries so the ACR relay would close to charge the batteries via engine alternator until I got to a dock with shore power ( roughly 15 minute) I then charged the batteries to full charge using the ProMariner. I can't say how much damage I did to the batteries but I haven't had an issue with them. I went to the boat this week (in storage) and when I checked battery condition the analog gauge at the panel was reading 12.7 V after a month of sitting. There may be hope Ethan give it a try. I wasn't going to throw the towel in on 550.00 worth of batteries without giving them a chance.

Sorry this happened. I do have a question so I don’t have the same thing happen to me. On my 2014 Cutwater I have two heaters like you. The refers are off for the winter. If power is cut off the heaters don’t work. Was your inverter on?

Yes my inverter was in charge mode.

Interesting. My Pro Mariner has a toggle switch. Shore Power/Charger, off, Inverter. I cant have the inverter on with it charging.

AZtoVA":33gsotyc said:

Interesting. My Pro Mariner has a toggle switch. Shore Power/Charger, off, Inverter. I cant have the inverter on with it charging.

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The pro mariner functions can be confusing. Here is how it works. With the toggle up if you are plugged into shore power then the charger will work and the automatic transfer switch kicks in to give you 110v. However, when there is no shore power and the toggle is up the inverter is in standby mode and charger is disengaged. You will notice every few seconds the analog meter will bounce a little. This is because it is hunting for a draw. If there is no draw then the inverter stays off. If there is a draw then the inverter will liven up and stay on. Hence, Ethan had the toggle up while on shore power to get his 110 volts. Then he lost shore power, the inverter went into standby, it saw a draw from his plugged in electrical appliance and the inverter started to deliver 110v using the batteries.
When the toggle switch is in the down position you are manually turning the inverter on and it is providing 110v regardless of a draw.
So unfortunately, Ethan had the perfect storm, inverter in standby getting shorepower and charger on. He lost power, charger went off, inverter went on standby, detected a draw, turned on, thereby depleting his batteries.

knotflying, thanks for this information. It clears up a lot for me.

Let me suggest you try a BatteryMINDer. It "blows" the sulfate coating off the surface of the lead plates -that's the deep sdcientific explanation :mrgreen:
They come in several flavors. I have the cheapie $68 dollar wall wart version (was 40 something when I bought it). It has recovered a number of batteries that were "dead", less than 6 volts. A couple came back up to full capability, and a couple were maybe 85-90% but useable here on the farm. That is a $480 save this year alone (roughly) of Group 31 for starting diesels. And I still have the charger which is almost always being used to pep up a battery that isn't quite what it used to be.
For the boat, I would isolate the battery set in pairs and let the BatteryMINDer cook on the pair for 3 to 6 weeks. Then do the other pair, etc.
Of course, you can do them in singles - or even the full set (might take a bit longer).
For long term maintenance just let it pulse on the entire house set when you are not using the boat.

knotflying":3g1n6tge said:

So unfortunately, Ethan had the perfect storm, inverter in standby getting shorepower and charger on. He lost power, charger went off, inverter went on standby, detected a draw, turned on, thereby depleting his batteries.

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I had this happen when the boat went into the yard for bottom paint, although I'm not sure where the draw was coming from since (I'm 99% sure) I had all breakers off at the panel.

knotflying":3g1n6tge said:

When the toggle switch is in the down position you are manually turning the inverter on and it is providing 110v regardless of a draw.

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Next time the boat goes into the yard, I was planning to turn off all the red disconnect switches instead of relying on the panel. Is there no other way to prevent the inverter from flipping on?

jaredjensen":1hubii7l said:

Is there no other way to prevent the inverter from flipping on?

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Ah, was just reviewing some reference photos of the boat, and I see the middle setting on the charger remote is "off". I suppose this might do the trick, although the remote switch is in an easy place to get accidentally flipped. In fact, when I picked up the boat from the yard, I noticed it was in inverter mode, which I am positive I didn't do.