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Battery maintenance

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dalelargent
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USA
198 Posts

Initially Posted - 04/23/2017 : 16:02:28

I have two AGM batteries in my bank. They stay charged with a solar panel year-round. They are at least 6 years old as they were on board when I purchased.

What maintenance, other than checking connections and posts for corrosion, should I be doing?

And if I need to check the cells' "water" level, how do I open the cells? Specifically, my batteries have what appear to be plastic hex nut shaped covers, about the size of a quarter, but are totally flush into the battery case. Are they sealed batteries?

I recognize there may be different opinions on this, but when do folks start replacing batteries simply due to age? Ever? Only after symptoms appear?

Thanks in advance...

1989 c25 WK/TR #5838
1998 Catalina 36 mkii
1983 Vagabond 14

islander
Master Marine Consultant

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USA
4018 Posts

Response Posted - 04/23/2017 : 17:22:30

AGM batteries are maintenance free so they don't require topping up of the water/acid. 6 yrs is good but they are probably getting close to replacement time. As with all battery's their capacity diminishes over time and will eventually not hold a charge. If they still hold a charge then use them. I have had a battery last for 9yrs once but usually I get about 7 yrs if you treat them well.

Scott-"IMPULSE"87'C25/SR/WK/Din.#5688
Sailing out of Glen Cove,L.I Sound

Voyager
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5352 Posts

Response Posted - 04/26/2017 : 06:57:47

If you want to test them you can do some simple testing:
1. Current draw test or
2. Take them to your local auto store - many offer free battery testing
To do a current draw test, I will get a 12VDC lighting fixture with a 25 W incandescent light bulb. This will draw about 2A.
I measure the battery voltage before, say 12.8VDC. Then I'll connect the lamp to the battery and let it run for 10 hours, maybe overnight.
This would require 2A x 10 hours, or 20 AH discharged.
A group 24 offers about 75AH and a group 27 has 90 AH. So for a group 27, this is 20 out of 90. But we are told never to discharge your battery more than 1/2 way, so 20 out of 45.
If the battery were discharged by 45AH, the voltage should read 11.7VDC
So using a little math, if you discharged your battery by 20/45 between 12.8 and 11.7 it should be sitting at:
.44444x1.1 + 11.7 = 12.1888 or about 12.2VDC
If your battery volts reads significantly less than that, (like below 11.5), then your battery is a candidate for retirement.
That said, if it still starts your engine and runs your lights, it it ain't broke don't fix it!
Do you have a pull cord on your outboard?

Bruce Ross
Passage ~ SR-FK ~ C25 #5032

Port Captain � Milford, CT

dalelargent
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USA
198 Posts

Response Posted - 04/27/2017 : 13:27:10

Bruce (and others),

Thanks so much for the input and experience.

It is so cool that we have so many different skills among us as a community...like how Bruce knows all of that theory and math!

I think I will do the load test just to have done it...for the experience.

Yes, my batteries seem to be operating perfectly thus far...and I DO have a pull cord on the Honda...which I use every once in a while just to make sure it works smoothly.

Dale

1989 c25 WK/TR #5838
1998 Catalina 36 mkii
1983 Vagabond 14

dalelargent
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198 Posts

Response Posted - 05/24/2017 : 23:22:07

I jinxed myself! After all of that thoughtfulness about maintenance, I launch my boat with two fully charged batteries. Now, three weeks later, one of them holds only 4.5 volts. Sheesh!

I do acknowledge they are 6-7 years old...

Other than the inconvenience of the other battery failing on me in the (near) future, any reason not to be frugal and replace only one at this time?

The second battery in the bank checks out fine, even though it's the same age. Maybe I can get one more season out of it, and at $250+ for an AGM....

1989 c25 WK/TR #5838
1998 Catalina 36 mkii
1983 Vagabond 14

OLarryR
Master Marine Consultant

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USA
3439 Posts

Response Posted - 05/25/2017 : 04:09:31

If you run your batteries , independently, with each on separate loads, then no issue running the old battery as long as feasible - Until it is ready for replacement. However, if you normally have both batteries running together for same loads, then you have some thinking to do whether to replace it now. The fact that the old battery is right now fully charged and working satisfactorily, makes the case for delaying replacing it - If it ain't broke, then why fix it. But the concern is that unless you have a battery combiner (or battery separator) wired between the batteries, the new battery will wind up working harder to run the loads as the old battery loses it's charge and at 6-7 years old, that will be happening starting now or during the next year or so. You may be okay for another year but then again, over the course of average service life of a battery (6. 7, 8 years ?), keeping it for one more year isn't going to make much difference cost-wise, except...shelling out the money now vs a year or so from now. You are still going to pay. Replacing it now gains you peace of mind...but eeking another year or more out of it...there is some satisfaction gained from that as well. Well, maybe...if you keep checking it's voltage, you can keep it till it is apparent it cannot maintain it's battery vol5tage close to the new battery.

During charging, unless the solar panel charges each battery, independently, the same issue is going to start happening - The panel will wind up charging the old battery more than the new one as the old battery's voltage starts to drop and becomes marginal. So, I am wondering if the new battery will get charged up to it's initial full battery charge and standing voltage.

Larry
'89 Robin's Nest#5820, Potomac River/Quantico, Va
http://catalina25.homestead.com/olarryr.html

islander
Master Marine Consultant

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USA
4018 Posts

Response Posted - 05/25/2017 : 06:26:17

As Larry said, As long as you keep them separated no harm will be done with having an old battery. But Never mix old batteries with new ones in the same bank( Hooked together). While it seems like this would increase your overall capacity, Old batteries tend to pull down the new ones to their deteriorated level. Another thought might be to use flooded batteries. They cost much less, Need very little maintenance ( check water once or twice a year, 5min.?) More forgiving to over/under charging and last just as long. There is no spillage in today's flooded battery's like in the past unless you turn them up side down. AGM's are expensive and IMHO the little benefits you might get from them don't justify the cost difference.

Scott-"IMPULSE"87'C25/SR/WK/Din.#5688
Sailing out of Glen Cove,L.I Sound

Edited by - islander on 05/25/2017 06:34:41

dalelargent
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USA
198 Posts

Response Posted - 05/25/2017 : 09:38:33

OK, all things in balance I will spring for 2 batteries.

And will consider the flooded. I was under the impression that AGM's are significantly better for sailboats, but perhaps that is old info....

1989 c25 WK/TR #5838
1998 Catalina 36 mkii
1983 Vagabond 14

OLarryR
Master Marine Consultant

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USA
3439 Posts

Response Posted - 05/25/2017 : 09:49:37

As Scott said, the flooded batteries are more forgiving in hpw they get charged and how abused, but you have to occasionally add water and ....there is a possibility that if and when removing them,you have to be careful not to rest them directly on your upholstery because any water/acid leakage that is settles on the outside perimeter , if it touches the upholstery, may permanently stain of damage it.

AGMs - I decided to go for them when I changed out my flooded batteries. No more water to add....but were expensive. So far, I have had no issues charging them. With AGMs, and old chargers or old solar panel regulators, should have a setting for AGMs since AGMs are charged somewhat different (voltage - wise) compared to flooded batteries.

Larry
'89 Robin's Nest#5820, Potomac River/Quantico, Va
http://catalina25.homestead.com/olarryr.html

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