Batteries: Do I Have to Change All of Them?

[Alecadi]

The Admiral is saying that we should have named all our boats: " Money Pit".. This one then should be " Money Pit IV"..

So there I'm again , still learning, 14 month before retiring and starting the cruising life ("if we still have some money left "-- says the Admiral)

Batteries:
-one 12v dedicated to cranking only
-House bank: 4x 6v 200Ah each Prevailer Gel Cell, for a total of 12v and 400 Ah

One of the 6v Cell gel got an intern short...

So I have to change it , and soon.

The friend helping me on the electricity, in the boat, told me that having old batteries joined to a new one the new will constantly discharged into the old ones (at least 5 years old) and that I be better changing the 4 of them...

But those gel cell are very costly.... even changing them for another brand (with only 180 Ah) still cost quite some money..

My question is: " Do I have really to change them all 4?"

[meyermm]

YES your friend is giving you good advice. Apart from technical reasons you will find them all going one after the other so you might as well get it over with now. They are already overdue I am sure some will come back with the my battery lasted 5,6,7,8 etc years but they are the exceptions not the average.

[daddle]

Well your friend is right and wrong. Most actively cruising boat batteries are pretty worthless after 5 years. You can mix older and newer batteries. That discharge myth is not true if the batteries are basically sound. I'd get deep-cycle flooded cells, far cheaper for the punch than gel and AGM.

[Capt Phil]

I'm with you, Daddle... I would go with a new suit of deep cycle floods as you are are going cruising full time within a year or so... cheers, Capt Phil

[AnchorageGuy]

I have to also agree. The best practice is to replace 6volt batteries in pairs but if you are sure the second battery of the pair is in good shape, you can replace just one. I also agree that wet cells are the best bang for the buck. We typically got 7 to 8 years out of a pair of wet cell 6volts and we find them for about $85.00 per battery. Chuck

[barnakiel]

You can replace just one but the new one will be dragged down by the old ones. It is best practice to replace all in the same bank, but when not practicable or possible, one only can be replaced.

I would replace the whole bank before any serious cruising and one only if you are 'tied to the dock'.

b.

[Pblais]

If you can regulate the charging AGM's are the Best bang for the buck over the long haul. Battery prices don't include the cost of recharging. AGMS' swill win on the long ahul the down side is you best regualte the charging properly or pay the penalty. It's true for flood batteries too but more so with an AGM.

I don't agree that replacing one battery is worth the cost savings. One bad cell will cause the whole bank to over charge and thus trash the rest sooner rather than later. So you save some money up front but later replace the whole bank later. You lose the money on the the one off soon when the rest go bad any way.

If you use the boat a lot them that is a serious factor. If you don't use the boat except on several long trips per year then you can do anything and not be that bad off.

You should be able to tell when one 6 volt flood is headed south if the water levels are not equally going down at the same rate within one bank. Replacing one battery earlier can work but if it is late in the process then the damage was already done.

If the bank is already weakened one battery trends to the the norm and will die sooner rather then extending the life of the rest. The worst battery rules the charging cycle. It's not about how much it costs at that level. I run 4 - 6 volts as one bank but I can cut out 2 if one battery goes bad. It becomes the problem of know which one is bad.

[S/V Alchemy]

Originally Posted by Alecadi

But those gel cell are very costly.... even changing them for another brand (with only 180 Ah) still cost quite some money..

My question is: " Do I have really to change them all 4?"

1) Yes, change them now. Use a pair of old ones, if you can stand the weight forward, as separate windlass batteries/"spares". Not needed if you don't make passages or hang out in lagoons.

2) Do you have a compelling reason to stick with gels/AGMs? If not, putting lead/acid is 1/3 the price, and you won't spend much putting them in boxes. Usually, the reason to get AGMs is so you can lay them sideways under the sole or under cabin berths and get that weight centered where access isn't needed. But lead acid is simpler and arguably more durable, especially if you look at the better golf cart battery makers like Trojan and IF you can deal with occasional hydrometer readings and putting a turkey baster of distilled water in them now and then.

I average six years with crap auto-grade lead-acids, but I pulled 18 year old Trojans that weren't quite dead out of my steel boat when I bought it.

I was impressed and as I have access to the tops of any battery I choose aboard, I'm going with lead-acid, likely forklift-style 6 V bigguns.

[S/V Alchemy]

Originally Posted by Pblais

If you can regulate the charging AGM's are the Best bang for the buck over the long haul. Battery prices don't include the cost of recharging. AGMS' swill win on the long ahul the down side is you best regualte the charging properly or pay the penalty. It's true for flood batteries too but more so with an AGM.

I would agree with this if the charging sources are limited, but in these days of flexible solar panels and efficient wind generators, as well as Honda 2000s or small 3K gensets, there is generally a "multi-point solution" to the problem of charging that means the higher acceptance of AGMs isn't as critical to the fair-sized cruising boat.

Obviously, draw down of amps/hours comes into play, as does the habit of leaving the boat sitting for some time. AGMs shine in regard of fast, higher voltage charging and resistance to voltage drop over time. I love my little Harley AGM I use to power my tender's lights, for instance. But the premium that is easy to pay for a race boat, say, is harder to justify for a well-equipped cruiser, as is the problem of availability.

Charging regimens are a function of a variety of sources and "opportunities", combined with a thorough audit of usage. If you over build your bank, and keep the draw downs in the 60-90% range, the fact that it's hard to push that last 15% into a lead-acid isn't going to matter.

A race boat isn't going to carry four 4Ds. A cruiser can consider it, plus the means to spend most of the day stuffing wind and sun amps into them.

[noelex 77]

If they are the Sonenschein batteries they are very good. On my first boat they lasted 16 years. On my current boat the PO idea of battery management was to drain them to flat before starting the generator. They still lasted 11 years.
So your batteries may only be in middle age.
I would do a capacity test and see how they are holding up.

A good option is to select the best 2 batteries and keep these. It is better to have these in a separate bank. It is very helpful for a cruising boat to have 2 separate banks of house batteries (3 banks in total with the starting batteries). It means you can mix batteries of different ages (and even chemistries with a bit of juggling).
2 separate house battery banks of different ages means they are unlikely to all fail at once.

It is very unwise to mix an old and new 6v battery in series to make 12v. So you will have to throw out one battery.

[pteron]

Originally Posted by S/V Alchemy

Charging regimens are a function of a variety of sources and "opportunities", combined with a thorough audit of usage. If you over build your bank, and keep the draw downs in the 60-90% range, the fact that it's hard to push that last 15% into a lead-acid isn't going to matter.

If you consistently charge to only 90%, you are going to suffer more sulfation.

The initial cost of the batteries is only one part of the equation but the easiest to see and be swayed by.

[Alecadi]

oops I have a lot of info to digest here...
First conclusion is that I've rather change them all anyway as we will be cruising out and finding good 6v would be more difficult.
The fact is I don't know the exact age of the batteries (they were already in the boat when we bought her).
The present one are indeed Soneinschen Prevailer. But they cost a fortune. The new ones are coming from Defender at almost half the cost. But 10% less Ah.
Good idea to keep the best 2 out of the reaming 3 as "spares"
But should I keep them on charge? Or what?
And thank you all for the sound advices.

[noelex 77]

Originally Posted by Alecadi

oops I have a lot of info to digest here...
First conclusion is that I've rather change them all anyway as we will be cruising out and finding good 6v would be more difficult.
The fact is I don't know the exact age of the batteries (they were already in the boat when we bought her).
The present one are indeed Soneinschen Prevailer. But they cost a fortune. The new ones are coming from Defender at almost half the cost. But 10% less Ah.
Good idea to keep the best 2 out of the reaming 3 as "spares"
But should I keep them on charge? Or what?
And thank you all for the sound advices.

The Soneinschene batteries have low self discharge. So they are fine with an occasional top up charge.
I would be weary of cheap gel batteries the cycle life is often poor. If you want to get inexpensive batteries wet golf cart batteries from a company like Trojan are the best choice.

[Alecadi]

Originally Posted by noelex 77

The Soneinschene batteries have low self discharge. So they are fine with an occasional top up charge.
I would be weary of cheap gel batteries the cycle life is often poor. If you want to get inexpensive batteries wet golf cart batteries from a company like Trojan are the best choice.

Well 300 $ a piece, I don't call that cheap. But I understand that this is a relative notion. What is cheap for some is not for others...

[btrayfors]

Your house bank is about 400AH now with the gels. You can get four 6V golfcarts which will give you ~ 450AH for about $320 (Costco/etc.) or about twice that for four T-105 Trojans (they've gotten really expensive; some feel they're worth it, others don't, and prefer the $80-100 varieties).

Either way, for $320-$600 you've got new flooded batteries for the house bank.

Take care of them, and they'll give you 4-6 years of good cruising performance (not 8-15 years as some have claimed).

Neglect them and/or mistreat them and you'll only get 1-2 years before replacements are required.

BTW, if you're just going to hang out in Marathon or Miami for the next year...mostly in marinas with shorepower available, then just remove the offending gel battery and the 2nd worst one, leaving two gels or about 200AH. That should be enough for dockside and "light" cruising.

Then, about 3 months before you take off for cruising, get all new batteries. DO NOT GO FOR PRICE ALONE. Quality is important, but so is freshness. Even new batteries can be badly sulfated if they've been sitting without charging for some time, particularly flooded batteries which have a self-discharge rate of about 5% a week in warm weather. Be sure to buy fresh batteries from a reputable place. Even better, beg, borrow, or steal a good battery tester (like the Midtronics series) and check the capacity of new batteries in the store before buying them.

I'm convinced that, in part, the various claims as to longevity of batteries derive from the original condition of the batteries as delivered from the store, and few sailors have sophisticated testers to really know how good the batteries are to begin with. Voltage alone is not an indication of battery health, nor is specific gravity -- both of these are indications of state of charge (SOC), not capacity.

Bill