Depth of Discharge Myth?

[Dockhead]

Originally Posted by witzgall

There should be a huge "It depends" in this. For boats with small battery systems, then perhaps. Once thing to consider is that many boat owners have limited boating time, and they may also be paying somebody to replace the batteries.

For many boat owners, the difference is not :Good or long life", but "Good or really cut short at the most inopportune time" scenario.

I realize this may not be a average Cruisers Forum member.

Chris

Again the narrow small boat perspective from KMacdonald.


A perfectly reasonable perspective for his use case. But not for me with almost $3000 worth of lead on board!!

[kmacdonald]

Originally Posted by witzgall

Again, no conclusions, but I am also leaning on the premise that time left in PSOC is more important than the depth, but the depth is also a measurable factor. I don't think it can be ignored. I do think it may be possible that we move that "Do not cross 50%" line downward somewhat. Certainly not to 20%, but maybe somewhere between 30-40%, depending on the PSOC time. This is a hypothesis, nothing more at this time.

Chris

Yes. That makes sense. I've been saying it for years but the dinosaurs are still entrenched and clinging to old ideals. Lets not forget that LA batteries have been improved over the years and don't behave exactly like your daddies LA batteries did. Trojan has "smart carbon" batteries designed to lessen the harmful effects of PSOC cycling. Car batteries last 8 or 10 years now, not the usual 3 years that they did 20 years ago.

[kmacdonald]

Originally Posted by witzgall

I realize this may not be a average Cruisers Forum member.

Chris

You're right. He's WAAAAAAAAAAAAAY beyond that. Batteries just don't have to be a significant expense of boating. Service providers will want to make you think it is so they can sell you a $10k gourmet power system. The fact is it's not necessary.

[kmacdonald]

Originally Posted by witzgall

For many boat owners, the difference is not :Good or long life", but "Good or really cut short at the most inopportune time" scenario.

I realize this may not be the average Cruisers Forum member.

Chris

Fear mongering. LA batteries rarely fail in a catastrophic manner. They die a slow and peaceful death.

[a64pilot]

I’m sitting in a “nice marina” in Jacksonville, it seems at least once a week I see a “mechanic” carrying a couple of West Marine batteries to a boat to replace them, it’s never been more than a couple, always West Marine brand and seem to all be sealed, so I assume AGM.

95% or better of boaters know nothing at all about the bank batteries, and of course their only way of knowing they are charged is when the green light comes on, and the few that have monitors didn’t install them, don’t know how they work, and don’t reset them etc.

It’s astonishing that batteries last as long as they do, or for that matter that cars do.
Nearly everything now is not maintained, you use it until it breaks, then buy another, and if your successful, you buy a new car or boat or whatever every few years, that is the 21st Century.
I know people who do no maintenance what so ever to their cars, they just get a new lease every couple of years, and in their way of thinking any maintenance is a waste of both time and money.

Point being is that to most batteries are consumables, like fuel in the tank, when the engine doesn’t start one day, you call the mechanic and he comes down the dock with a West Marine battery or two in the cart and your good until the next time it won’t start.
To the boating industry, we are odd balls, and I’m surprised that there are as many products as there are for maintaining a bank.

[a64pilot]

Originally Posted by kmacdonald

Fear mongering. LA batteries rarely fail in a catastrophic manner. They die a slow and peaceful death.

Your correct, but to many who pay no attention whatsoever to their batteries, it’s a sudden death, yes it has been losing capacity over time etc., but they don’t notice until it won’t start the engine, so to them it “suddenly died”

[Dockhead]

Originally Posted by kmacdonald

Fear mongering. LA batteries rarely fail in a catastrophic manner. They die a slow and peaceful death.

Never had a shorted cell?


I've had this twice in the last 10 years, and I know a guy whose boat was burned down as a result of such an incident. It's a very common failure mode. What's dangerous about this is that the battery voltage immediately falls by 1/3 (1/6 in case of 6-cell, 12v battery), which will cause the battery charger, if it's attached, to pump up the voltage attempting to charge it. If there's not temperature sensor involved, this will boil out the remaining cells and pretty soon you have melt down.


It's a good reason to replace batteries early, before they really get near the end of their lives, and this increases the cost of using lead batteries.

[kmacdonald]

Originally Posted by a64pilot

Your correct, but to many who pay no attention whatsoever to their batteries, it’s a sudden death, yes it has been losing capacity over time etc., but they don’t notice until it won’t start the engine, so to them it “suddenly died”

Nothing a $20k gourmet system and a bottle of snake oil won't cure.

[kmacdonald]

Originally Posted by Dockhead

?? Do you have much experience with lead acid batteries? Never had a shorted cell?


I've had this twice in the last 10 years, and I know a guy whose boat was burned down as a result of such an incident. It's a very common failure mode. What's dangerous about this is that the battery voltage immediately falls by 1/3 (1/6 in case of 6-cell, 12v battery), which will cause the battery charger, if it's attached, to pump up the voltage attempting to charge it. If there's not temperature sensor involved, this will boil out the remaining cells and pretty soon you have melt down.


It's a good reason to replace batteries early, before they really get near the end of their lives, and this increases the cost of using lead batteries.

I think I see one burning down now! You better get a $30k gourmet system to monitor for that. WiFi enabled so it can send you an e-mail of impending doom. All joke aside, that's what insurance is for.

[Dockhead]

Originally Posted by kmacdonald

. . All joke aside, that's what insurance is for.

Insurance is no substitute for competent operation, and understanding risks of using any given system, including lead acid batteries.

[kmacdonald]

Originally Posted by Dockhead

Insurance is no substitute for competent operation, and understanding risks of using any given system, including lead acid batteries.

Sure it is. Almost all accidents come down to human error. People make mistakes and pay insurance companies a premium to assume the risk. That's how it works.

Now in a perfect world you'd be right but not many boaters want to make the boating experience a science project. They want to hop in the boat and turn the key. If you cruise to remote locations then it becomes necessary to be self sufficient but that's not the norm. Most boats are attached to the dock with an umbilical cord.

Do you really have $3k worth of lead batteries on your boat?

[mako]

Originally Posted by witzgall

I do think it may be possible that we move that "Do not cross 50%" line downward somewhat. Certainly not to 20%, but maybe somewhere between 30-40%, depending on the PSOC time.

There's no law of physics that says a FLA battery cannot be discharged below 50%. It's just an accepted rule of thumb where its cycle-life starts to greatly reduce. But I think that is based on the average consumer battery, like an inexpensive Costco golf cart battery.

If you look at the discharge/life cycle chart of a heavy duty industrial 2V battery you'll see that they can discharged 100% with 900 cycles reported.

From a practical point of view, if you're not a world cruiser, then buy some inexpensive Costcos and discharge them all you want. Buy half the number you normally would then drain them down to the floor. If they die in 3 years then go buy some new ones.

I think we have to remember that when it comes to boat systems and specs, it's really a matter of how each of us will use the vessel - whether it's batteries or displacement or the dreaded anchor-discussion.

PS - Speaking of "disposable" batteries. Our car batteries here have to be replaced yearly. When your car's engine room is sitting in the sun at 140-150 degrees you don't tend to get much life out of rubber hoses or batteries.

[Dockhead]

Originally Posted by kmacdonald

. . . not many boaters want to make the boating experience a science project. They want to hop in the boat and turn the key.

Depending on the use case, it is not possible to make something as complex as a cruising boat, at least not one capable of extended autonomous operations, a device you can "hop in" to and "turn the key".



Not all boaters day sail out of marinas, returning to shore power every night or at least every Monday morning.

Originally Posted by kmacdonald

Do you really have $3k worth of lead batteries on your boat?

Yup. Weighing more than a quarter of a metric tonne. And it's not really enough for my use case. You should not universalize your own experience so much. Other people use their boats in very different ways.

[thinwater]

If this were an anchor thread, it would be go up two sizes to 100 pounds because you could be anchoring off Patagonia vs. Fortress, and oversize chain vs. Dyneema.
Otherwise, hard to tell apart.
-----



I've had enough different boats to understand that everyone here has a point. With each boat, my answers to these questions would have been different. Does weight matter? Not to everyone.

• How big is the bank? A single group 24 battery is minutes to change, but a big bank of traction batteries is a project.
• How critical is power failure? An outboard can be pull-started, a big diesel is a problem.
• What charging sources are available? How many days between full charging?
• How often is the boat anchored-out? Are we talking thousands of cycles or hundreds during the life of the battery?

There is simply no way that one answer is right for everyone. On my last boat battery maintenance was serious. On my F-24 I have one slim 50W panel, weight matters, and the battery is a throw-away.

[Dockhead]

Originally Posted by thinwater

If this were an anchor thread, it would be go up two sizes too 100 pounds because you could be anchoring off Patagonia vs. Fortress, and oversize chain vs. Dyneema.


Otherwise, hard to tell apart.


I've had enough different boats to understand that everyone here has a point. With each boat, my answers to these questions would have been different.

• Does weight matter? Not to everyone.
• How big is the bank? A single group 24 battery is minutes to change, but a big bank of traction batteries is a project.
• How critical is power failure? An outboard can be pull-started, a big diesel is a problem.
• What charging sources are available? How many days between full charging?
• How often is the boat anchored-out? Are we talking thousands of cycles or hundreds during the life of the battery?

There is simply no way that one answer is right for everyone.

Of course. A common problem in discussions on here is that many people assume that everyone else uses their boat the same way they do, and argue strenuously to solutions which fit only their own use case. It's a waste of time.


One reason why the battery problem hasn't been solved better up to now is that a significant proportion of boats do actually sit in marinas on shore power most of the time and don't cycle their batteries more than a couple dozen times at most a year. Another group have good solar installations which treat lead acid batteries like royalty, giving them all the finish charge they need every day.



So it is a specific use case which requires real performance from batteries and requires enough knowledge to know how to operate them correctly. That is people who sail off the beaten track and those who live at anchor for months at a time, and those who sail in places where marinas don't even exist. Probably some people with boats on moorings, too.


So those of you who don't have any challenging task for batteries -- maybe just move along; nothing to see here. Some of us do have really challenging tasks for batteries, and who have banks large enough to make a mistake in operation really expensive. That is the use case, which this thread is about.