What count as a cycle (battery life)

[john61ct]

Originally Posted by gauvins

If batteries are always kept between, say, 70% and 85%

If lead, that in itself will murder the bank, IMO means you don't care about longevity.

Except apparently for Firefly Oasis, but they still need proper care.

[john61ct]

Originally Posted by Sojourner

Hmmmm I was told by my PO to not cycle my banks below 80%. I have enough solar and wind that the batteries live at 100% (trickle charging when I'm not there, no shore power even in marina, just the renewables). In the morning they're down to 90%, by 11 am pretty much topped back up....

That means you're carrying too much dead lead weight.

Or if no dino-juice charging, you're well positioned to outlast poor solar conditions.

[john61ct]

Originally Posted by gauvins

Based on quick back of the envelope calculations, AGM batteries would be twice as cost effective as flooded batteries.

The opposite is the case. What is causing you to believe that?

[john61ct]

Originally Posted by gauvins

Expected life of a battery is typically expressed in cycles. Say 200 for lead, 600 for AGM

AGM is lead, maybe you mean FLA?

Quality FLA usually lasts longer than AGM, especially in sub-optimal conditions.

And the maker, batt **quality** matters more than category, a bank of 2V Rolls / Surrette FLA cannot be compared to a bunch of 12V AGMs from Amazon or big box retail

[Dockhead]

Originally Posted by Pete7

. . . but has 4 x the cycles, too good to be true perhaps?
. . .

If I'm reading the literature correctly, they only claim 600 cycles at 50% DOD, which I think is typical of semi-deep-discharge lead acid batteries and less than a typical golf cart battery.

As others have said, however, what is claimed and what is real may be two completely different things, so I think it's right to take all this with a grain of salt.

One thing that bothers me about AGM batteries is that they can't be (AFAIK) equalized. So if something happens and they get accidentally discharged and left, or you go through a period where you have no chance to get them up to 100%, they may be permanently damaged, whereas a good heavy duty golf cart battery can be nursed back to health with equalization.

[john61ct]

Originally Posted by gauvins

Thanks for your input.

Based on quick back of the envelope calculations, AGM batteries would be twice as cost effective as flooded batteries. So it would seemed as a no brainer. It probably is for full time cruisers. However, the expected life of an AGM bank would be so long that calendar life would become a significant factor in our case.

I am just about to renew our battery bank. We consume about 100Ah/day and produce nearly as much with our solar panels. Plan is to get 3x230Ah deep discharge lead batteries. Based on what I read here, we'll make sure that they are regularly fully charged. We'll be happy to get 5 seasons. And then we'll see.

You'll get longer life and best value out of 6x 6V FLA GCs rather than 3x AGM 12V.

Can't really beat Duracell (actually Deka/East Penn) around $200 per pair from BatteriesPlus or Sam's Club

[john61ct]

Originally Posted by Dockhead

One thing that bothers me about AGM batteries is that they can't be (AFAIK) equalized.

Lifeline can be, but only manually, closely following their protocol.

Excellent **if** you really need AGM, but will still cost a lot more per year per AH compared to FLA, especially if not being well coddled.

[Maine Sail]

Originally Posted by Dockhead

So I now occasionally let my batts go down to 40% or even 30% -- mostly on multi-day passages under sail, when I'm having a great sail and just don't want to start up a diesel engine.

Again, there is nothing wrong with this so long as it is occasionally and you get back to 100% SOC shortly there after. On offshore passages cycling below 50% simply makes more efficient use of your charging systems because you will be in bulk longer and bulk is the most efficient stage of charging.

In other words if you've decided you need to run the motor once every 24 hours, for 1 hour, you will store more energy in the batteries, in that hour, by cycling deeper than 50%. This is because the bank will likely not attain absorption (will depend upon your charge rate of course) and nearly every Ah you put in will be usable on the way back out. If you have a 100A of charge current and discharge to 80% DOD then charge for 1 hour you can expect to extract about 99 +/- Ah's to wind up back at the same DOD.

If however you cycle to 50% and run the engine for 1 hour you will get less usable energy because you will most likely become voltage limited and current acceptance will taper off rapidly.

The batteries I capacity test, that are regularly cycled to 80% DOD, live very short lives (Firefly & LFP not included). The testing of these batteries has shown that this is not at all all in-line with what the cycle life charts suggest as the differences between 50% and 80% DOD in throughput Ah's. The manufacturers know this and this is why most strongly recommend 50% as max regular DOD. The occasional dips to 70% or 80% DOD are not the immediate death some assume it is but the deeper you routinely go, in the real world, the worse off it gets.

[john61ct]

Originally Posted by Dockhead

When I am off the grid, I do not even ATTEMPT to get up to 100% every day. It simply makes no sense as it would require hours and hours of generator run time at light load.

If you full-timed off-grid then you'd find a way.

Even being at sea or on the hook just a week at a time, just a little solar would be well worth the investment.

Genny in the morning gets you to 80%, maybe 90% if it's cloudy, just 10-20A is plenty to handle "the long tail" rest of the day for even a big bank.

[Dockhead]

Originally Posted by Maine Sail

You just can't compare lab cycles to real world. There is no equivalent because in a lab the data they present to us for "cycle life" is not run to mimic real world use. If your use mimicked the lab you could see lab like results but this is just not possible.

We also should not get hung up on cycle life graphs. They are not created from actual testing at those DOD's they are done using best guesses and then "extrapolated" based on "lab" data. In the real world the deeper you go the faster you loose capacity and degradation is quite exacerbated / amplified below about 50-60% SOC (why most manufacturers suggest 50% as max DOD, despite their graphs showing otherwise based on throughput).

Sulfation due to PSOC use, chronic under charging, incorrect charging and temperature are what usually kill marine batteries. You can't translate this to lab cycles only practice good battery care and hope for the best.

I have customers who can get 13-17 years out of GEL batteries and others who destroy the same battery in 2 years. I have customers who can get 12-13 years out of golf car batteries and others who can destroy the same batteries in 4-5 years. I have customers who can get 10 years out of premium AGM batteries and others who can destroy the same battery in 1-2 years.

Some best practices for longer life:

• Charge to full as often as possible

• If only charging when cruising get back to 80% + at least with each charge cycle and get to 100% as soon as you can there after. Weekly to 100% as a minimum guideline but 3-6 times per week, to 100% SOC, will rather dramatically improve cycle life.

• For flooded deep cycle (thick plate) break the batteries in by cycling them deeply a few times (down to 11.7V) and recharge to 100% SOC after each dip to 11.7V. Do not continue 11.7V discharges beyond about 4-10 cycles. These deep cycles help form the pathways in the cells. Most AGM batteries will come up to full Ah potential in about 3-7 cycles so no real break in needed. Flooded batteries take a lot longer 25-50+ cycles.

• Do not regularly cycle your bank below 50% SOC. The occasional dip to 80% DOD is fine but try to follow that up with a 100% recharge ASAP. The less deep you regularly cycle the more cycles you will get, with caveats such as PSOC and getting back to 100% SOC often enough. I know many AGM makers initially launched into the market claiming 80% DOD was fine. It was all about $ to Ah to cycles for marketing purposes against flooded batteries. All but Odyssey/Enersys have changed their tune on this and 50% is now the max recommended DOD by most all AGM & flooded battery manufacturers. Firefly is one exception and the battery is designed & intended to be used and cycled daily to 80% DOD. I am doing this now on a number of boats and so far the batteries held up to the first three season of this abuse. (Firefly's can't be compared to other lead acid batteries)

• Size your charging or alternator for a bare minimum of at least 20% of bank capacity. Bigger is better with AGM but 20% of "C" should be the bare minimum for AGM's. eg: A 400Ah bank should ideally have an alternator capable of at least 100A so that when hot it will still hit the 20% minimum.. Odyssey AGM's (Also Die Hard Platinum which are re-branded Odyssey) want to see a minimum of a .4C charge rate. This is 40A for a 100Ah battery. High charge rates for AGM batteries are yet another piece of the cycle life puzzle than should not be omitted. FDC batteries can be charged at .15C to .3C depending upon brand.

• Dock charging. Leaving batteries on unattended "constant charge" can be a poor choice for them if the charge equipment is not up to snuff. Many chargers are not as "smart" as they claim. Charge to full then disconnect is often safer or setting a permanent float when dockside so it can't bump to absorption every time a load kicks on..

• Use temperature sensing on all charging sources; alternator, battery charger and solar if equipped. Temp sensors need to physically mount to the battery and not measure "ambient temps" near the charger or controller.

• Use smart chargers, controllers, regulators etc. that can be custom programmed to your specific batteries. For example with some not so good solar controllers every day begins with a new absorption cycle needed or not. If the AGM's are full this can be damaging to the battery because their self discharge is so low.

• Proper float voltages are absolutely critical to AGM & GEL longevity and it also needs to be temp compensated. One size fits all smart chargers that use "egg timer" algorithms are usually not well suited or matched to all batteries.. If a charger does not come standard with, or offer, a physical external temp sensor, and also allows you to create a custom program, just walk away. Most GEL, AGM, WET dip switch chargers are very, very poorly suited to many batteries as the three settings rarely if ever line up with your batteries voltage profile for float and absorption.

• Use a case mounted alternator temperature probe and external regulators. AGM's, GEL's & even large flooded banks can take huge amounts of current and can burn down wimpy alternators when asked to produce full output for hours on end.

• Use an alternator capable of running high loads at high temps for long periods of time if needed. Despite marketing attempts to make folks believe otherwise, there is no such thing as a constant duty small case alternator. This means you can still fry a heavy duty alternator by running at at full output for hours on end. Most sailboat AUX engines ship with small case alts.

• Properly wire voltage sensing if you want fast charging. On 98% of "high output" alternator installations I see voltage sensing is incorrectly wired thus sending the regulator into CV/voltage limiting far earlier than it should be. Incorrect voltage sensing robs you of the fastest charging potential.

• Consider a serpentine/ribbed belt kit for the alternator. Dual belts will work too but they often wear unevenly and finding accurately matched pairs is getting tough.

• Alternator and charger wiring should be sized for the least voltage drop that you can reasonably attain. If using an alternator and external regulator utilize the bank sensing circuitry so the regulator can compensate for slight voltage drop in the system wiring, over current protection and terminations. Voltage sensing needs to be properly wired to positive and negative battery terminals..

• Program your alternator regulator so that you can fully charge your bank (if you were to run the engine long enough). The factory settings are way to wimpy for most banks and they can suffer from premature-floatulation (dropping to float far to early). The factory programs are what I often call lawyer safe & cut back to float far to early. Only choose regulators that can be fully custom programmed...

• Use smart chargers that can remain in float even with dockside loads on such as a fridge. Many chargers can be re-triggered into another absorption cycle just by a fridge compressor kicking on. Better yet choose one that allows a custom program for you to create a permanent "float" setting when you're not there. Some have a power supply setting that permanently locks it in float mode.

• Equalize your batteries routinely if PSOC cycling. Sulfation becomes permanent fairly quickly and once it is hard, clustered and dead no amount of EQing will bring it back. Wait too long and you've missed the window.

• If you will be PSOC cycling, most cruisers are, choose the highest safe absorption voltage the manufacturer allows for. Eg; if the allowable range is 14.4V to 14.8V choose 14.8V..

• In the off season charge to 100% SOC then store the batteries in a cool location disconnected from each other and the vessel..

• Check electrolyte regularly on flooded batteries and be very careful to not contaminate the cells when they are opened.

• Choose quality batteries, not all batteries are created equal.

That's a start anyway..

Wow! You are a font of knowledge!

Just one question --

You are holding with the popular wisdom that you should not discharge below 50%, at least not often. What is this based on? Does something happen between 50% and 80% DOD which is not reflected in the DOD vs cycle life charts? Because if you take the charts at their word (which maybe we shouldn't do), there is no difference in life putting the same number of AH's through the battery cycling it between 10% and 80% DOD as there would be cycling it between 10% and 50% DOD. If the charts are just wrong, I wouldn't be surprised, but inquiring minds want to know why! And how we know!


As to my boat --

I have beautiful battery boxes which fit perfectly in two very convenient spaces on my boat, which were, unfortunately, designed for 12v 110ah Varta leisure (ick) batteries. No way to get golf car batts in those boxes, and it would be expensive to have new boxes made up, and not clear whether they would even fit.

Therefore, I use Trojan 27TMX 12v batteries, which are labelled "deep cycle" but which are just high quality leisure batteries. Trojan claim 600 cycles at 50% DOD. These batteries are obviously not ideal for long distance cruising off the grid, but they give reasonable service, far better than the old Varta ones.

I used to get 3 years out of a set of these, but that was when I kept the boat on a mooring with no shore power, so they were sitting partially discharged most of the time, and were used and cycled whenever I was on board, which was most of the time. Two years ago I moved from the mooring to Cowes Yacht Haven with unlimited free power (yay), and we shall see how long the batteries last. The current set is now two years old and seem to be still good as new. I'm off cruising four months out of every year and mostly off the grid. But now in the winter they are hooked up to a Victron Multiplus with a proper "storage" voltage float mode, which I think extends the lives of the batts (the Victron also gives automatically a shot of absorption charge once a week when the boat is not being used).

When these are worn out, I think I will finally go to LiFePo, if I still have this boat.

[john61ct]

Originally Posted by Dockhead

should not discharge below 50%, at least not often. What is this based on? Does something happen between 50% and 80% DOD which is not reflected in the DOD vs cycle life charts? Because if you take the charts at their word (which maybe we shouldn't do), there is no difference in life putting the same number of AH's through the battery cycling it between 10% and 80% DOD as there would be cycling it between 10% and 50% DOD.

The lab cycles on the chart are based on 100% every time, that - along with many firms' marketing dishonesty and artificial consistency - is why they aren't IRL applicable.

No one can "cycle" to such low top marks and get any decent longevity, every proposed "average cycle" should strive to get back as close as possible to 100% Full - as defined by endAmps - as often as practical, ideal at least a few times per week.

And you are right, there is no magic black and white line **at the low end** with drastic consequences.

But carrying less lead therefore consistently going to say 30% SoC rather than trying to stop at 50% will result in a **much** shorter lifespan.

Which is not a problem, as long as the owner is consciously choosing that, carrying less weight at the cost of replacing the bank more frequently.

The exact cost tradeoffs involve too many variables IRL to pin down precisely, but the shape of the DoD/cycles curve gives a rough idea.

[a64pilot]

You can and should equalize Lifeline AGM batteries.
If nothing else their Manual is full of knowledge, they have done a lot of testing and don’t mind spreading the knowledge.
They are a battery you want, if your the type to read and follow directions, cause they spell out exactly what you need to know.

I’ve had a Lifeline bank going on four years now, and I disagree with the equalize manually and carefully part, yes maybe you shouldn’t push a button and go to town, but you don’t have to watch and adjust anything. Maybe you ought to be on board just in case something goes wrong, but in truth I don’t see anything that is more likely to go wrong than regular charging of a bank.
After a long discussion with Justin years ago, I equalize when we are on the hook monthly, and then not for the full time. Very quickly after I begin equalizing absorption amps drops to a very low amperage, well less than 5 amps, and if you think about it for just a minute, you can’t really cause anything bad to happen with a bank with less than 5 amps, it’s just not enough energy to start a runaway.
Now I assume that since I draw so few amps on equalization, that I’m either badly sulphated or not sulphated much at all, as my bank seems to have lost only about 10% capacity from new, I go with barely sulphated.

However based on when we make water and wash clothes etc, I get to 100% SOC about every three days, even in cloudy weather. 100% SOC is to me when acceptance at absorption voltage is less than 3 amps.

[gauvins]

Originally Posted by Maine Sail

How do you figure this?



It depends a lot on what batteries you choose

I am currently in Europe. Varta is a widely available brand here. Their 230Ah lead acid is rated at 200 cycles .5 DoD and goes for 300 euros. Their AGM 260Ah is rated at 800 cycles .5 DoD for 680 euros.

Doing the maths, that's 23 000 Ah for 300 euros (77 Ah/euro) vs 104 000 Ah for 680 euros (153Ah/euro). So almost twice as many Ah in an AGM.

[john61ct]

So look at other brands that make better FLA.

Rolls sells internationally.

[Dockhead]

Originally Posted by Maine Sail

. . . The batteries I capacity test, that are regularly cycled to 80% DOD, live very short lives (Firefly & LFP not included). The testing of these batteries has shown that this is not at all all in-line with what the cycle life charts suggest as the differences between 50% and 80% DOD in throughput Ah's. The manufacturers know this and this is why most strongly recommend 50% as max regular DOD. The occasional dips to 70% or 80% DOD are not the immediate death some assume it is but the deeper you routinely go, in the real world, the worse off it gets.

OK, that's just what I needed to know.

So much for my theory based on the charts.

Thanks very much.