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Discussion Starter · #1 ·
Went down to the boat today and noticed that my house bank is dead dead dead... No reading at all on the battery monitor.... The shore power was apparently switched off last Fri., and today, Wen. they are flat. The reefer was left on... The batteries are 12v lead acid from 2018, and this is the first really deep discharge. Does anyone think there is any chance they will still be usable?
 

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Do yourself a favor and install one of these on the panel feed: https://www.bluesea.com/products/7635/m-LVD_Low_Voltage_Disconnect

This assumes the loads controlled from your panel do not draw more than 65A.

Then the loads will be shut down before the battery is dead. Of course, you would still have a stinky reefer to deal with...

Mark
 

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Went down to the boat today and noticed that my house bank is dead dead dead... No reading at all on the battery monitor.... The shore power was apparently switched off last Fri., and today, Wen. they are flat. The reefer was left on... The batteries are 12v lead acid from 2018, and this is the first really deep discharge. Does anyone think there is any chance they will still be usable?
I think chances are poor. If it does it only will last a few months of use based on my experience, but good luck.
 

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Irrationally Exuberant
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I'm with Barry. Give it a try. But these are 4 year old lead acid batteries. Probably already seeing some reduction in AH, and this is only going to reduce that. Time to start budgeting for some new batteries in the near future.
 

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Discussion Starter · #8 ·
Thanks for the responses guys.. I'm not going to be too broken up about it, I'll probably replace them with two 6v, AGM if my battery charger can still do the lead acid start battery.....
 

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How long they are flat makes a difference. This was not that long.

That said, it can take time, quite a few cycles and some equalizing. You've lost a percentage, but likely only 10-15% or so.
 

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Dirt Free
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Whether they can come back or not is largely determined by their voltage (which you don't mention) and their electrolyte level. What does "dead, dead, dead" mean ?

If they hit less than 11V it's unlikely they are coming back ... for long.
If they hit 10.5V they ain't coming back.
 

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Discussion Starter · #12 ·
Whether they can come back or not is largely determined by their voltage (which you don't mention) and their electrolyte level. What does "dead, dead, dead" mean ?

If they hit less than 11V it's unlikely they are coming back ... for long.
If they hit 10.5V they ain't coming back.
Dead, dead, dead, means my battery monitor was without power, no display at all.... They did come up to voltage today, and even started the motor. I guess I'll have to fast cruise at the pier to see how they do overnight...
 

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Dead, dead, dead, means my battery monitor was without power, no display at all.... They did come up to voltage today, and even started the motor. I guess I'll have to fast cruise at the pier to see how they do overnight...
... So you would have to know the minimum voltage for the display. (A multimeter can read low voltages... but it has its own battery). And time discharged really does matter. I've had flat batteries that came back reasonable well.

But I would NOT try them out after a single charge. Let them charge for a week, equalize them, and only then see what you've got.
Rectangle Slope Plot Font Line
 

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I'm a little surprised no one commented on my discharge graph. 100% discharge is defined as about 10-10.5 V (I forget the exact figure), so the amount of damage really does depend on how low you go, which generally requires some time. For example, the reefer would have cut out at some minimum voltage, as would some other parasitic loads. Self-discharge continues, but at a diminishing rate. Getting to really low voltages takes a while unless some restive loads are still connected (incandescence lights or a motor with non-electronic controls, such as a sump pump). The longer the time and the lower the voltage, the more the battery corrodes.

No simple answer. You won't find graphs for >100% discharge, which is what we are talking about.
 

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Discussion Starter · #18 ·
I'm a little surprised no one commented on my discharge graph. 100% discharge is defined as about 10-10.5 V (I forget the exact figure), so the amount of damage really does depend on how low you go, which generally requires some time. For example, the reefer would have cut out at some minimum voltage, as would some other parasitic loads. Self-discharge continues, but at a diminishing rate.
Now I'm sorry I didn't think to put a meter on the batteries... With no voltage showing on the battery monitor, I assumed they were dead and not coming back, but I didn't consider that the reefer would cut out at low voltage... I'll have to look for the manual and see what that voltage is...
 

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Now I'm sorry I didn't think to put a meter on the batteries... With no voltage showing on the battery monitor, I assumed they were dead and not coming back, but I didn't consider that the reefer would cut out at low voltage... I'll have to look for the manual and see what that voltage is...
Yeah, in cold climates, lots of electronics cut out at 50% SOC because the voltage drops in cold weather. Lots of things drop out just a little below 12V, because in normal weather, that is when the battery is below practical use. IT can make winter sailing tough if you don't warm the battery bank.
 

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The compressors used in boat reefer systems have a default shutdown voltage of 10.4V. This is adjustable from 9.6V to 11.3V with resistors.

If your reefer shut down, then they likely hit 10.4V unless you changed this value by intentionally inserting a 14-82ohm resistor in between the T terminal and the thermostat.

Mark
 
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