Re: Wet Cell Batteries



You didn't mention how old your batteries are, or who made them.  With any voltage setting questions I always go to the manufacturer's literature as the primary source since different batteries are... well... different.  Not all flooded batteries are exactly the same.  A half gallon of water into 12 batteries over a month doesn't sound very excessive to me.  that's less than 30 ml/cell/month.

Equalization is an important part of getting certain types of batteries (especially flooded cell batteries) to live out their full life span. This is sometimes called "desulfateing."  It can be tough to get a good equalization charge using a solar system, but it can be done by bring them up to full before the brightest part of the day with the genset.  Again, your battery maker is a good source for what an equalization charge should look like and how to know how much is enough.  If one hour is not sufficient, you can just start another cycle right away.

Some battery makers recommend monitoring SG as a way of determining when the equalization charge is complete rather than using a time based recipe.

It is generally accepted that replacing one battery out of a set is bad practice.  Having batteries of significantly different ages means they are being charged very differently, and that it bad for the whole string.  Sometimes it can't be avoided, but in general it is a bad idea.

Check the connections, make sure they are all clean and tight.  Then do a full equalization charge, as per the makers recommendation, and see if those SG values come closer together. Then think about running an equalization as part of your standard maintenance program. 

Bill Kinney
SM160, Harmonie
Little Harbor, Abaco, Bahamas

---In amelyachtowners@..., <sailor63109@...> wrote :

I'm trying to understand the condition of our house battery bank.  I'm definitely not a battery expert.  We have the original Dolphin Battery Chargers (100A and 30A).  We use the 30A at the dock and the 100A with the generator.  We also have a Victron Blue Solar 100/30 with 630 watts of solar panels.  The installer set it at 28.8V Absorption and 27.6V Float (Position 2).

First:  The 12 Group 31 house batteries use about 0.5 gallons/ that excessive?  I'm wondering if the MPPT controller is overcharging the batteries.

Second:  How close to replacement are we?

I checked the specific gravity of all cells recently (see the attached spreadsheet).  I read that a new, fully charged cell should be at 1.265, and is discharged at a SG of 1.120.  The best cell tested at 1.265 and the weakest cell at 1.145 (corrected for temperature).  The average SG of all cells was 1.226.  This SG corresponds to 75% state of charge from what I read.  At SG of 1.190 the battery is at 50% SOC and battery #3 has three cells in that range.

Third:  Should I just replace Battery #3?

Fourth:  I've read that when the difference between cells in a battery is greater than 0.03,0 the batteries would benefit from equalization.  My Dolphin chargers are not adjustable (at least as far as I can tell).  The MPPT has an equalization function that will run for an hour.  Will that be sufficient?

Thanks for your input,


Wanderer, SM#477

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