Measuring Specific Gravity of Batteries

[dlochner]

MS,

It's a long winter here in central NY with little access to my new to me Sabre 362. The 4 6v batteries and one 12v battery have been in the boat for several years and it has sat on the hard for nearly three years. When I finally get to the boat in the next month or so, I'd like to check the condition of the batteries by measuring the specific gravity of the electrolyte with a refractometer.

In the interest of reducing time spent hanging upside down in the lazarette, how many of the 36 individual cells should be sampled to get a fair idea of the batteries condition? I'm thinking that a ⅓ would be a decent sample. What are your thoughts?

Thanks,

Dave

 

[Maine Sail]

MS,

It's a long winter here in central NY with little access to my new to me Sabre 362. The 4 6v batteries and one 12v battery have been in the boat for several years and it has sat on the hard for nearly three years. When I finally get to the boat in the next month or so, I'd like to check the condition of the batteries by measuring the specific gravity of the electrolyte with a refractometer.

In the interest of reducing time spent hanging upside down in the lazarette, how many of the 36 individual cells should be sampled to get a fair idea of the batteries condition? I'm thinking that a ⅓ would be a decent sample. What are your thoughts?

Thanks,

Dave

4 6V = 12 Cells - Do them all
1 12V = 6 Cells - Check OCV, top up with water, equalize.. If you really feel the need check the SG.

SG only tells you if you have cells getting out of balance. An ROCV (resting open circuit voltage) reading will give you the same "bank level" SOC reading but can't identify cells getting out of balance. Check SG if you notice issue, or once per year of coastal or bi-yearly if cruising.

 

[dlochner]

4 6V = 12 Cells - Do them all
1 12V = 6 Cells - Check OCV, top up with water, equalize.. If you really feel the need check the SG.

SG only tells you if you have cells getting out of balance. An ROCV (resting open circuit voltage) reading will give you the same "bank level" SOC reading but can't identify cells getting out of balance. Check SG if you notice issue, or once per year of coastal or bi-yearly if cruising.

MS,

Thanks for the advice. I'm hoping to get a couple of more years out these batteries and then replace them before the "retirement cruise."

Dave

 

[Benny17441]

A single bad cell will make a battery worthless even if the other cells in it test well. If you are solely utilizing the "specific gravity test" then you must test all cells to get any significant results. If on the other hand you hand you have measured the output voltage of all batteries and determine that they seem to be OK then a cell sampling may yields and average value for the estate of health of the entire bank. My question would be why settle for an average value when you could rather easily test all 18 cells and get an actual health measure for all.

 

[patrick33308]

The 6V battery's are golf cart battery's ?
If so, dont waste your time, go to Sams Club, Walmart, Advanced Auto and replace them. As a general rule they last about 3 years and then start acting up so if I were you, I get new ones.
PS, I use them in my H33.5, 3 years is the average.

 

[Maine Sail]

The 6V battery's are golf cart battery's ?
If so, dont waste your time, go to Sams Club, Walmart, Advanced Auto and replace them. As a general rule they last about 3 years and then start acting up so if I were you, I get new ones.
PS, I use them in my H33.5, 3 years is the average.

Something is very wrong if all you get is three years. I See an avg min of 5 years and a max of about 10. Most 6V golf cart batteries, on the boats I work on, are 6-8 years. Lots of variables but three years on 6V GC2's is not even within the realm of normal cycle life..

 

[patrick33308]

Thank you for the reply. The last set of batterys in my boat were West Marine 6V golf carts, lasted 3 1/2 years and the sides bulged out on 3 of them.
The set before them were bought at a large battery outlet in Ft.Lauderdale off SR 84 I got about 4 years before some of the cells went bad.
So at 3 years I change them.................

 

[Bill Roosa]

I agree, 3 years is really bad.
Another way to check the balance or for bad cells is to use a volt meter. Take off the caps, stick the meter probes in the electrolyte in adjacent cells and read the cell voltage. Don't touch the plates!!! For the end cells use the battery terminal for one probe and the electrolyte for the other. All should read with in 0.05 volts of each other for that battery.

 

[gettinthere]

Our 12 volt golf cart batteries, yes Trojan makes 12 volt batteries for golf carts also, are on year 6 and still going strong. Lots of people are getting 10 years out of 6 volt flooded batteries. Two 3 year deaths sounds like a problem not of the battery's making.

 

[gettinthere]

Since this is about specific gravity, perhaps 'someone' has bought and tested every SG tester out there and can post a 20 page report on the efficacy of various brands?

 

[Don S/V ILLusion]

Since this is about specific gravity, perhaps 'someone' has bought and tested every SG tester out there and can post a 20 page report on the efficacy of various brands?

Be careful what you wish for...

Thanks for using the word "battery's" in the proper context. I just read another post in which someone questioned the location of "battery's", something about "ware" to locate a "waist" holding tank, whatever that is... You have restored my faith.

 

[dlochner]

A single bad cell will make a battery worthless even if the other cells in it test well. If you are solely utilizing the "specific gravity test" then you must test all cells to get any significant results. If on the other hand you hand you have measured the output voltage of all batteries and determine that they seem to be OK then a cell sampling may yields and average value for the estate of health of the entire bank. My question would be why settle for an average value when you could rather easily test all 18 cells and get an actual health measure for all.

It's about balancing time, risk, inconvenience, and cost. The boat is about 150 miles away and I'll have a 200 mile trip through the Erie Canal to its homeport. There is little risk if a bank fails while we're on the canal and minimal inconvenience. Even if all the house batteries fail, any small town along the way will have a auto parts store where we can get a battery to power the house. If I can save some time by randomly checking the cells, then'll I have more time to devote to getting to other tasks. Once the boat is home, I can and will do a more thorough check of the electrical system and the other systems. On the electrical upgrade list is a Balmar Smart Guage, replacing the old diode based battery combiner, and installing a smart plug, not necessarily in that order. I'm hoping to avoid replacing the batteries until we leave on a year long cruise in a couple of years.

As for battery life, last summer I replaced my 9 year old WM Group 24 starting battery. The 8 year old Group 24 Die Hard Deep Cycle still had enough life in it to serve as a starting battery.

 

[Bill1565]

Something is very wrong if all you get is three years. I See an avg min of 5 years and a max of about 10. Most 6V golf cart batteries, on the boats I work on, are 6-8 years. Lots of variables but three years on 6V GC2's is not even within the realm of normal cycle life..

+1. 3 years is sub normal life .

 

[Maine Sail]

+1. 3 years is sub normal life .

For group 24, 27 or 31 12V batteries that is even below normal. But for 6V that is way below normal.

There are two solutions:

#1 Spend the money and throw it at batteries ever three years

#2 Address your system, care & charging issues.

Properly charged and cared for the bare minimum I expect from GC2's is 5 years and this is with marginal care, poor charging and poor use practices. Three years indicates an extreme system situation...

 

[Benny17441]

I don't know if it is the heat and humidity or the fact that we sail year around but batteries here in Florida do not seem to last more than 4 years. I'm sure someone out there can boast getting 7-8 years out of his but I'm talking about average usage with minimum maintenance. I have never sat down to keep data on the number of cycles I get from my batteries but sailing all year round I'm sure that I do go through that finite number of cycles perhaps twice as fast as someone who only uses their boat 6 months out of the year.

 

[patrick33308]

Good comments Benny, thanks.
And, yes, I use the boat all year round, several times a week and at times for weeks at a time thru the Bahamas.
Hence the short life of the golf carts................

 

[joshua131960]

Good comments Benny, thanks.
And, yes, I use the boat all year round, several times a week and at times for weeks at a time thru the Bahamas.
Hence the short life of the golf carts................

I believe part of the reason for a shorter battery life may be linked to the amount of time you are charging them. A boat on shore power at the marina with the charger running constantly will have a shorter battery life span that a boat that is drawing down and recharging deep cycle batteries on a regular bases.

 

[fruivita]

Be careful what you wish for...

Thanks for using the word "battery's" in the proper context. I just read another post in which someone questioned the location of "battery's", something about "ware" to locate a "waist" holding tank, whatever that is... You have restored my faith.

Don, your taking this to seriously. There just trying to get a answer to they're question. Two funny.

 

[Morgan donor]

dlochner,
I sail a Morgan 383 out of Fairhaven, a few miles from you. My batteries: Exide CG2's 6V's winter on board up here in the great white north. They'll be in their 8'th season whenever the freakin ice melts! So to everyone's point: Something ain't on your Sabre.

My set up is simple; Xantrex Trucharge 20 on shore power - in season. I run low draw Nicro 12v fans continuously and I have refrigeration, which takes the batt's down to 50% in 24 hours when off the grid. I keep the (distilled) water level where it needs to be religiously.
Winter:
No draw on the batteries at all after final charge & equaliization when I winterize. During the winter, I hook a Honda 2000 to my shore power which runs the Xantrex at least once during winter for 3-4 hours. Compared to many boats my system is stone age.

I think my secret is simply a good 3 stage battery charger (Xantrex).
When I sell the boat I take the charger! (Its over a decade old)
FWIW

 

[dlochner]

dlochner,
I sail a Morgan 383 out of Fairhaven, a few miles from you. My batteries: Exide CG2's 6V's winter on board up here in the great white north. They'll be in their 8'th season whenever the freakin ice melts! So to everyone's point: Something ain't on your Sabre.

My set up is simple; Xantrex Trucharge 20 on shore power - in season. I run low draw Nicro 12v fans continuously and I have refrigeration, which takes the batt's down to 50% in 24 hours when off the grid. I keep the (distilled) water level where it needs to be religiously.
Winter:
No draw on the batteries at all after final charge & equaliization when I winterize. During the winter, I hook a Honda 2000 to my shore power which runs the Xantrex at least once during winter for 3-4 hours. Compared to many boats my system is stone age.

I think my secret is simply a good 3 stage battery charger (Xantrex).
When I sell the boat I take the charger! (Its over a decade old)
FWIW

MD,

I have two Sabres a 30 in Oswego and a 362 in Buffalo. The batteries on the 30 have done very well, 8 or 9 years. Store them on the boat fully charged for the winter and leave them alone till spring. The question I raised is about the 362, its new to me and I don't know the history of the batteries. With the boat in Buffalo 3 hours away, I want to make efficient use of my time while I'm in Buffalo. When the boat gets to Oswego, I'll have lots of time.

And, later this spring the 30 will go on the market.

Dave