water gone from one of the batteries

[GrowleyMonster]

Originally Posted by chuckg5

hello
we have an older vagabond 42 sailboat. the other day i finally checked the water levels, its been about a year since I've done that and found one of the new 6 volt batteries empty of water. i have 4 12 volt in series and the 2 6 volt in parallel in line with tthe 12 volts...All has worked fine for the last year except now, with a boiledout 6 volt. what changed or what could have happened?

So, did you actually mean four 12v batteries in PARALLEL? And a series string of two 6v batteries, in parallel with the 12v batteries?

I was assuming that you meant exactly what you said, I guess because I am used to working with higher DC voltages. Most boats use a 12v system. If you have multiple 12v batteries connected in parallel, then you get 12 volts nominal. If they are in series, you add the voltages to get bank voltage.

If you actually have a series string of two 6v batteries, in parallel with the four 12v batteries that are parallel connected, then it would be best to split the pair of 6v batteries off into a separate bank, assuming you are able to bring the dry one back to life.

https://www.trojanbattery.com/tech-s...y-maintenance/
The above link is a great place to start learning about batteries, especially flooded lead acid (FLA) batteries.

[chuckg5]

thanks for the replies! after filling it back up with water the voltage did return 12.8 at rest . having the boat for 18 years got me lazy

[boatpoker]

Originally Posted by chuckg5

thanks for the replies! after filling it back up with water the voltage did return 12.8 at rest . having the boat for 18 years got me lazy

1. Did you use distilled water ?

2. At rest voltage of 12.8 gives no indication of battery health. The chances of it
lasting long are slim.

[gonesail]

Originally Posted by boatpoker

At rest voltage of 12.8 gives no indication of battery health. The chances of it lasting long are slim.

yep. take it to an automotive store for testing. chances are good it is DOA.

[team karst]

Its good to get a read on the battery internal resistance. I dont know how accurate the testers are that dont have the big resistor/load.

[GrowleyMonster]

Originally Posted by chuckg5

thanks for the replies! after filling it back up with water the voltage did return 12.8 at rest . having the boat for 18 years got me lazy

Keep in mind that resting voltage is only an indication of SOC, or State Of Charge. Don't get me wrong, it is importat, because it tells you that you don't have a shorted cell. Capacity is likely significantly impaired, maybe permanently, or maybe it can be resuscitated. It needs a couple of full charge/discharge cycles to restore it even if it is a fairly healthy battery. If you have any way of equalizing the battery, you should do that, after charging and discharging a couple of times. You can do a load test if you want an actual number that tells you how much capacity remains in the battery.

Load testing an engine start battery or a "marine" battery is a bit different from load testing a deep cycle battery. If you take it into town for a shop to load test it, make sure they understand the difference. Most automotive shops don't have a clue what you are talking about, and will simply nod politely and take your money.

A 6v GC2 golf cart battery, which is a true deep cycle battery, typically has a capacity rating of around 215 or 220 amp hours AT THE 20 HOUR DISCHARGE RATE. So, if you divide 220/20 you get 11 amps. Theoretically you should be able to draw 11 amps for 20 hours on a fully charged battery to take it down to 0% SOC, usually regarded as 10.5 volts. You can do this test without a load tester if you have an ammeter that will handle that much current, or a shunt ammeter. You can get a cheap Chinese one, with shunt, for around $15 on amazon. Wire up DC loads in series until you get your 20 hour discharge current. The manufacturer might give capacity for other than the 20 hour rate. They might also give a number of minutes at a certain current. You can use that, if you like. You do the math. You will have to adjust the load periodically as the voltage falls off. Maintain that current and when you get to 10.5 volts note the time it took and what percentage of 20 hours (or other specified discharge time) you got. This is close enough to correct. Ideally you don't want more than about 15% difference in capacity between two batteries in series. If you only get 70% of the rated capacity, may as well toss it, anyway. Well, don't toss it. Take it with you when you buy new batteries, for the core charge.

I just scanned amazon looking for a load tester that allows you to set the desired discharge current and I didn't see one but I didn't do an exhaustive search. Just remember you are not looking for a load tester that gives you CCA and most automotive load testers give you CCA and not much else.

Here is some more reading for you.

https://www.element82.co.nz/faqs/cap...ting-batteries
https://www.foxtronpowersolutions.co...attery-is-bad/

https://www.youtube.com/watch?v=C2knGYucoyo

https://bobistheoilguy.com/forums/th...teries.338549/

[chuckg5]

wow, Growley... that's a lot of good info. i'm going to try some of that

[GrowleyMonster]

Originally Posted by chuckg5

wow, Growley... that's a lot of good info. i'm going to try some of that

Don't be disappointed if you are unsuccessful. But it is worth a try, as much as batteries cost these days; and the more you know about your batteries, the better you can maintain them and the longer you can go between purchases of new ones.

[MVDarlin]

Even my sealed. "No service" Optima AGM batteries need routine inspection. I just removed one from my battery bank that was too hot to touch! This has been in service about 3 years.

[ogalili]

Originally Posted by GrowleyMonster

So you are running 54 volts?

But as for the dry 6v battery it might be salvageable. Isolate that one, fill it just until the plates are covered, and charge it. Check the water. The battery should make water when it charges. If it takes a full charge, go ahead and top it up. Discharge it through a resistor or other load, and do another charge cycle. Then you should equalize. This is a controlled over-charge. Consult your battery maker's website for the correct equalizing voltage because NO "smart" charger will do a true equalization. The voltage simply will not go high enough. I use a large Variac and a rectifier from an old stick welder. Like I said it requires monitoring. Monitor voltage, battery temperature, and charging current. I use a shunt ammeter for current. Actually I have a 25 amp direct series connection ammeter but I haven't used that yet. There will be significant gassing. This should be done on deck or on the dock, nobody smoking or burning or welding nearby.

I ran a 48v bank of 6v GC-2 golf cart batteries on my e-boat and I equalized every couple of months and got 8 years of service out of them. I usually equalized the entire bank at 64 to 65 volts. As the batteries aged I started equalizing them individually at around 8.1 volts. The knob on the Variac must be adjusted to maintain the desired voltage.

Assuming your batteries are true deep cycle, in lieu of recommendations from the manufacturer's website, you might go by Trojan's recommendations. 2.7v per cell for equalizing. In fact the Trojan website has a lot of great information guidelines and tips on using deep cycle batteries.

Most "marine" batteries are not true deep cycle batteries. They are a compromise between good engine start performance and deep cycle storage performance. Just keep in mind that deep cycle and marine batteries are two similar but different critters.

Most yachties do not bother with equalizing or even know how to do it or even are aware that it is a thing. If the boat is taken out often, it isn't so important. The motion of the boat helps to prevent stratification of the electrolyte. One of the things that equalizing does is mix up the electrolyte.

At any rate, that particular battery needs special attention if it is to be saved and not cause problems being in parallel with the other 6v and in series with your 12v batteries.

Why the odd voltage? EP setup? Honestly I would just run 48v, which is 4 12v batteries in series. If you are going to go over 50V then you may as well go up to at least 96v for greater efficiency.

As for what could have made that battery go dry, hard to say from here. High current passing through that battery, maybe. Bad connections on its mate. Shorted cell or two. General neglect or mistreatment. Manufacturing defect. End of life performance issues. But if you replace it, also replace the other one that you have in parallel.

<EDIT> Now would be a good time to clean and retighten and grease all of your battery connections, and wipe down the case tops.

Do you equalize them while they are connected to your systems?

[ItDepends]

Originally Posted by chuckg5

hello
we have an older vagabond 42 sailboat. the other day i finally checked the water levels, its been about a year since I've done that and found one of the new 6 volt batteries empty of water. i have 4 12 volt in series and the 2 6 volt in parallel in line with tthe 12 volts...All has worked fine for the last year except now, with a boiledout 6 volt. what changed or what could have happened?

How to kill an expensive battery bank in one easy lesson.

Having one battery in a string totally dry probably has destroyed the rest of them as well. Why did this happen? Without details of your installation, wiring, and maintenance that is impossible to say. Could be just a bad battery that was ignored. Or it could be the setup inherently overcharged this battery to the preference of the others. Or you never properly equalized them. Or all of the above.

[GrowleyMonster]

Originally Posted by ogalili

Do you equalize them while they are connected to your systems?

No. I prefer to isolate the batteries. Some DC loads might be sensitive to overvoltage. And you should definitely isolate parallel batteries, too. When you have one problem battery in a series string (such as two 6V batteries connected in series) it should of course be isolated and equalized separately. I have equalized my entire 48v EP bank as a unit but as they got older I did start equalizing each battery separately. Batteries of the same brand, size/type, age, and health in a series string can be equalized in series but if there is any doubt, do each one separately. If any specific gravity is inconsistent with the rest, separate them. Don't try to equalize a parallel connected bank as a unit.

Don't forget to monitor case temperature, and after a couple of hours if charge current has not fallen off while at equalizing voltage, you should stop and check the electrolyte level because equalizing will cause considerable outgassing. Furthermore, it is a good safety practice to remove batteries to be equalized from the boat altogether, or at least to open deck. If you are struggling with 8D's or other very heavy batts, and removal is not practical, at least lay on additional ventilation.

At the end of an equalizing cycle always check the specific gravity. All cells should be pretty close to the same SG. Also, top up the water to the fill line at this time. When all your batts have been equalized, hook them up and connect your normal charger for float/maintenance.

[svfinlandia]

Originally Posted by Jammer

I would guess it was a shorted cell though usually I would expect that to have affected both 6v batteries in the string. As Cheechako writes, shorted cells are fairly common in FLAs.

That is sure a lot of battery capacity. You must have a very large boat.

My first guess would be a shorted cell in that six volt battery.
Personally, I would not try to recharge it. I would recycle it and replace it with a new one, but that is just me. If you do decide to fill it with distilled water and try to charge it, keep a very close watch on how warm it is getting during the charge.

When I am on my boat, I check my battery water once a week and when I’m not on the boat, I unplug the shore power or turn off my battery charger and let the solar powers keep the batteries triple charged.

Al, S/V Finlandia

[svfinlandia]

Originally Posted by boatpoker

I'm not so sure. I've never seen an internal short without a significantly swollen or distorted case..

But that is a sealed battery. If his was a sealed battery, where did the water go??

Al, S/V Finlandia