Wet Cell Batteries

Duane Siegfri

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/month...is 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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