Battery Data

Sep 20, 2015
123
Navigator 4200 Classic New Bern, NC
Hi everyone... It has been a while. I hope y'all are well these days.

I have a question or two about my battery bank (again). I am not sure about the overall health of my batteries. I have done a resting test; having left the batteries disconnected for 24 hours then reading the voltage... then reading the SG with a refractometer. The data from the house bank is attached in a picture below. A few weeks ago we went and anchored out, however, when we went to lift the dinghy with our davit crane, the winch (a 12v Dayton from Grainger), the motor strained, I assumed dropped the voltage, spiked the amperage, and tripped the breaker. The winch runs strong when connected to shore power, so I don't think it is that (but I have since replaced it out of an abundance of caution). Are my batteries in need of replacement? More below...

Backstory: We are a 42' planing motoryacht. I completely overhauled the DC system (with yall's help) five years ago. The DC system consists of two banks. The house bank is eight GC2 standard Penn 6v flooded golf cart batteries. The other is three 12v Group 27 dual purpose batteries that do starter duty for both motors and the genset. All batteries are five years old, but they have lived a very easy life. Due to various circumstances over these years (hurricanes and such) we have really only anchored out maaaaaayyyyybe five times? The remaining time, the batteries have been on a Sterling 60A charger (with temp probe).

I feel like there is some conflicting data here. The resting voltages seem okay, but the specific gravity says differently. Or am I reading that wrong? At anchor, the Victron gauge shows (if memory serves) 12.2v for the house bank. While there still may not be a ton of use in the near future, when we DO go out, I'd like to be confident that the batteries are in good shape. I am not totally against replacing the lot, I would hate to waste $1000 if they are still in decent shape. Is there something I am missing or another test I need to conduct?

Thanks!!
 

Attachments

Apr 8, 2011
768
Hunter 40 Deale, MD
Mainesail is the authority here, but my guess is you need to charge each bank to to float, rest them, and then run the 20-hour discharge test at their rated load down to 10.5 volts and see how many amp hours you get out of them. Then you'll know how much they've degraded in terms of holding a charge. Anything less than 80% of their rated capacity likely means they're toast.

The details of how to run this test, if you haven't read it before, are in this forum. Best to run them on a bench with the ability to put the exact rated load on them, but you can do it from the boat if you can attain/maintain the necessary load over 20 hours. I vaguely recall a shorter test that gives less accurate results, but I could be wrong.

Good luck.
 
May 24, 2004
7,129
CC 30 South Florida
Batteries do need to be used, keeping them with a low grade charging current for extended periods of time is not good as it will promote sulfating and a decline in capacity. My concerns with a 5 year old battery bank is that usually you can have one battery that has declined faster than the others and is bringing the whole bank down. I use a simple automotive type battery load tester to flush out any overly weak batteries. If it is just one or two I may choose to replace individually rather than the entire bank. You may be sacrificing some of the life of the new battery but in the entire scheme you may be extending the life of 6 or 7 others. I t makes really good sense in $$$. You can pick up one of those testers at Harbor Freight for under $15. I don't even disconnect the batteries from the bank to test them individually and it can pick out a weak battery.
 
Sep 20, 2015
123
Navigator 4200 Classic New Bern, NC
my guess is you need to charge each bank to to float, rest them, and then run the 20-hour discharge test at their rated load down to 10.5 volts and see how many amp hours you get out of them.

The details of how to run this test, if you haven't read it before, are in this forum.
I am not sure, using a quick forum search, I'd be able to meet what seems to be fairly strict criteria to do a proper bench test of all eight batteries (I am two hours away from the boat). I suppose I could bring the all home and test them over a week, but what do you use for a load? Does this test tell you more than specific gravity?
 
Oct 26, 2010
1,883
Hunter 40.5 Beaufort, SC
I am not sure, using a quick forum search, I'd be able to meet what seems to be fairly strict criteria to do a proper bench test of all eight batteries (I am two hours away from the boat). I suppose I could bring the all home and test them over a week, but what do you use for a load? Does this test tell you more than specific gravity?
A professionl "load" tester, like Maine uses will cost you a bundle. However, you can buy one over ebay for less than $50. The ones I've seen have been limited to either 150 Watts or 180 Watts which limits the size of the battery combination you can test. Since you have a bank of several 6V batteries you could separate each 12 volt group and thest them individually. Not sure how you'd interpret the tests. You can also insert a static fixed load resistor to get the variable load down to within the limit for the load tester. I bought one of these and it worked perfectly. Was it "calibrated" like Maine might use - NO. It was a darn site better than trying to turn on and off various loads to keep it even close to the right load for 20 hours straight. Good luck with that. It maintains a constant load (11.5A in my case} and automatically shuts off at a voltage you set (10.5 volts in my case). I was surprised how well it worked. The instructions are obviously written in Chinese and then translated so it takes a little experimentation to get all the settings right but once that is done the test was easly. To get a really accurate test you will need to control temperature too but I had it at home and had the room set at 70 degrees.

 
May 17, 2004
5,032
Beneteau Oceanis 37 Havre de Grace
+1 for the 20 hour load test as a way to get the most accurate idea of the true state of health. I use a cheap inverter (auto parts store style, anything that doesn’t a have a low voltage cutoff), powering an incandescent bulb on a dimmer. I use a shunt to check the battery amperage, and adjust the dimmer every few hours to keep it close to the right amount. It’s a bit of a pain but not too bad, although I generally only do one battery per winter. The device Smokey found its probably worthwhile to do more.
 
Feb 26, 2004
22,760
Catalina 34 224 Maple Bay, BC, Canada
Five years? Not bad, replace them. Last month, I just got six years, almost to the day, out of my house bank. Don't dunce around and over analyze this. If something isn't working because of poor power, and you've eliminated the something as the problem, the issue is the power.
 
Sep 20, 2015
123
Navigator 4200 Classic New Bern, NC
Five years? Not bad, replace them. Last month, I just got six years, almost to the day, out of my house bank. Don't dunce around and over analyze this. If something isn't working because of poor power, and you've eliminated the something as the problem, the issue is the power.
Yea... I get that to a certain extent, but doesn't it seem like replacing the entire bank is equivalent to cutting off your arm to treat a hangnail? Certainly a full replacement is on the list of possible solutions, however, with the data I collected, I was thinking that I should at least explore options.
 
Jun 11, 2004
1,621
Oday 31 Redondo Beach
I don't have an answer but am curious about the voltage. Your attachment show 12.76 to 12.8 but you say your Victron shows 12.2. Why is there that difference?
 
Feb 26, 2004
22,760
Catalina 34 224 Maple Bay, BC, Canada
Yea... I get that to a certain extent, but doesn't it seem like replacing the entire bank is equivalent to cutting off your arm to treat a hangnail? Certainly a full replacement is on the list of possible solutions, however, with the data I collected, I was thinking that I should at least explore options.
And those options would be? Look, my point was that either they are toast and/or soon to be useless hunks of lead, or they are not. You got five years out of them. If they're still OK, then what is your issue? If they are beggining to be questionable, only YOU can determine what risk you're willing to take, regardless of what anyone says. Hangnail? C'mon.

And all this load testing carp I keep reading about is a very, very hard way to do something that's really simple: check what the bank voltage is under load. Turn your fridge on, run a few lights, if you went to LEDs, turn more stuff on to attempt to replicate a reasonable load on your house bank. Then watch the voltmeter. I am NOT saying "Use the volts to measure the health of the bank." What I AM saying is that if your see a voltage SAG when charging is removed then your bank is on its way out. Period. After all these years.

I made up a simple spreadsheet last year because I was experiencing the same issues you described. It was a blank ss that I wrote in hourly amp load, amp hours used from my battery monitor, what was on (fridge, VHF, battery chargin devices, inverter, etc.) and kept track of it whenever I was on the boat away from shorepower.

I could clearly see, over course of the past year, that even with my "standard use" loads of the fridge and a couple of lights, that the voltage, which should have been above 12.5, started to drop to 12.4, then 12.3, then 12.1, etc. right away after I turned the engine off.

That was a clear signal to me that I had to get a new bank. I did. I have used the new bank now for two cruises and see the voltage with load staying above 12.5 for a long time. I forgot how it used to be. :) Like in GOOD.

This is a simple real world way to check what you have.

Denial was something I dealt with, too. I got over it and bit the bullet and now don't have this nagging worry in the back of my mind. It's like reefing...

And I didn't need any fancy schmantsy test gear. You don't either.

Good luck.
 
Sep 20, 2015
123
Navigator 4200 Classic New Bern, NC
I don't have an answer but am curious about the voltage. Your attachment show 12.76 to 12.8 but you say your Victron shows 12.2. Why is there that difference?
The 12.2 was the reading I was getting at anchor. The others were the resting voltage.
 
May 24, 2004
7,129
CC 30 South Florida
An automotive battery tester will test both 6V and 12V and it provides the load at the flick of a switch. It is portable and easy to operate. You can test the batteries in an 8 battery bank in around 10 minutes without having to disconnect them. The tester is a simple volt meter with a scale for 6 and 12V and the load is a carbon heating element activated by a spring loaded toggle switch. you can buy one at Harbor Freight for around $15. Just connect one cable to the positive and the other to the negative of each battery. There is likely a voltage feedback from the other batteries but when you flip the load switch it will tell you if that individual battery is good or weak. The tester pointer will drop to a red area in the scale if the battery is too weak. I have found this method to be good enough to pluck out a bad battery in a multi battery bank. Ok, 5 year old batteries are probably going to show weak but usable and the question whether to replace them all I would say depends on the type of sailing. If going in an extended trip you should replace them, but they would be fine if just out for the weekend you could postpone the expense for perhaps another two years. I purchased a golf cart two years ago and the seller told me the batteries were shot that I would need to replace them. I looked at the dates and they were only two years old. The cart indeed was slowing down after 15 minutes of running. I tested the batteries and found one bad one that failed the load test. Just replaced that one battery and the cart has been running strong for the past two years and I should get another year or two before replacing the whole pack.
 
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Sep 20, 2015
123
Navigator 4200 Classic New Bern, NC
An automotive battery tester will test both 6V and 12V
Certainly not trying to be argumentative, but if I recall correctly, hasn't Mainesail himself say not to use these types of testers? While fine for starter batteries, that they don't give an accurate representation of the status of deep cycle batteries. In fact, I used to have one, but gave it away when I read his take on them.
 
Oct 29, 2018
24
Hunter MH37 Mississauga
The 12.2 was the reading I was getting at anchor. The others were the resting voltage.
How many amps were you drawing and for how long since you shut the diesel down at anchor when you read the voltage? In other words, how many amphours had you drawn down from the batteries since you dropped the hook and cut the alternator? At 12.2V I'd (very very rough) estimate that you've drawn the batteries down to about 30% usable power remaining. As an example only...If you're running a fridge, freezer, ice maker, lights, etc for 8 hours, that could easily add up to 35amps x 8hours = 280Ah on a boat your size. You'll have to check the battery ratings, but if you have 600Ah of house capacity (remember, only half or 300Ah are usable on lead acid batteries), then you'd expect your voltage to drop by that much in that time drawing that much power. You'll need to check your amps drawn while on battery only and then estimate your usage at anchor. Your solution might be as simple as limiting your consumption or increasing your battery capacity (Ah).