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Old 31-05-2018, 16:57   #1
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What count as a cycle (battery life)

Expected life of a battery is typically expressed in cycles. Say 200 for lead, 600 for AGM, 1000 for lithium.

What counts as a cycle?

If batteries are always kept between, say, 70% and 85%, i.e. a mini cycle of 15%, would 6 such cycles count as a full cycle? Or what?

If a battery is kept fully charged during the off season (10 months a year in our case), does it mean no cycling no ageing at all?

All I could find were examples of cycles going from full charge to the suggested minimum for a given chemistry. Say 50% for deep discharge, 20% for AGM, 0% for lithium. (I know that one should avoid getting even close to these values in order to optimize battery lives, but I have no idea about the relationship between usual depth of discharge and life expectancy (expressed in total Ah stored and pulled from a battery)
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Old 31-05-2018, 18:02   #2
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Re: What count as a cycle (battery life)

Here's a typical cycles v DOD% chart.



The bottom line is that a battery has a finite total Amp hours throughput. The higher the DOD in each cycle, the lower the total AH you will be able to put through it throughout its life. From about 40% the DOD v cycles line is fairly straight, so total AH doesn't change much. However with DOD less than 40%, the curve bends up noticeable. The lesson from that is keeping DOD above say 30% will result in a large increase in the total Ah that the battery can deliver over its lifetime.


WRT a battery not being used 10 months of the year - there is another factor to be considered. Chemical changes will take place and internal resistance will increase with battery age regardless of how it is used. That means that if you only use your battery for 2 months and keep it topped up the rest of the year, it will not last 6 times as long
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Old 31-05-2018, 18:11   #3
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Re: What count as a cycle (battery life)

Quote:
Originally Posted by gauvins View Post
Expected life of a battery is typically expressed in cycles. Say 200 for lead, 600 for AGM, 1000 for lithium.

Lab cycles are not very representative of real world cycling. I see customers routinely destroy 1200 cycle rated batteries in well under 150 cycles.


Quote:
What counts as a cycle?

What ever DOD you discharge to then back to 100% would be a cycle as a battery manufacturer defines it in a lab. You can have shallow cycles or deep cycles, most have a mix plus PSOC use.


Quote:
If batteries are always kept between, say, 70% and 85%, i.e. a mini cycle of 15%, would 6 such cycles count as a full cycle? Or what?

This is a cycle but it is a PSOC cycle or partial state of charge cycle where you're not returning to 100% on every cycle. PSOC use is not good for any lead acid battery but it's a reality for most. We know from PSOC testing that in as little as 30 PSOC cycles, on standard AGM batteries, we can see permanent capacity losses ranging from about 30% to about 8% depending upon brand and quality.



LiFePO4 could care less about PSOC use and in fact it prefers not to be held in the upper SOC ranges but LFP really has a lot of other issues that can limit cycle life. Just like lead acid they need to be charged & used correctly or cycle life suffers.


Quote:
If a battery is kept fully charged during the off season (10 months a year in our case), does it mean no cycling no ageing at all?

Even with no cycling there is still calendar aging. The cooler the storage area the better for the battery it will be.


Quote:
All I could find were examples of cycles going from full charge to the suggested minimum for a given chemistry. Say 50% for deep discharge, 20% for AGM, 0% for lithium. (I know that one should avoid getting even close to these values in order to optimize battery lives, but I have no idea about the relationship between usual depth of discharge and life expectancy (expressed in total Ah stored and pulled from a battery)

When outside a lab, the more often you get back to 100% SOC, with lead, the longer the life will be. I have seen banks regularly cycled to 50% that are returned to 100% SOC 3-4 times per week easily outlast the battery that's "shallow cycling" between 75% SOC & 90% SOC but only getting back to 100% SOC perhaps bi-weekly or longer. Battery temp also plays a role the warmer the battery over its life the shorter the life it will have..
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Old 31-05-2018, 18:23   #4
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Re: What count as a cycle (battery life)

Maine Sail, thank you for the concise and informative reply. Similar questions had been concerning me as well.
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Old 01-06-2018, 00:08   #5
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Re: What count as a cycle (battery life)

Just to emphasize what was said before.
Lithium should be stored at below full chsrge.
Bery low self discharge also means that if you are sure that the batteries have no load, you may be able to leave them off any charger.
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Old 01-06-2018, 00:24   #6
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Re: What count as a cycle (battery life)

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....
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Old 01-06-2018, 04:36   #7
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Re: What count as a cycle (battery life)

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Originally Posted by StuM View Post

WRT a battery not being used 10 months of the year - there is another factor to be considered. Chemical changes will take place and internal resistance will increase with battery age regardless of how it is used. That means that if you only use your battery for 2 months and keep it topped up the rest of the year, it will not last 6 times as long
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.
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Old 01-06-2018, 05:08   #8
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Re: What count as a cycle (battery life)

Wow, great information!! I've been wondering about this myself.

Stu says, if I understood him correctly, that it's the total AH throughput of the battery which uses it up, with the caveat that not all AH "use up" the battery at the same rate -- when the battery is below 40% SOC, it will be "used up" at a faster rate.

Stu, did I get you correctly there?

And MaineSail -- you didn't really answer the question, I think -- sure the makers DEFINE cycles like you say, but what is it that uses batteries up? Do you agree with Stu?

I guess it boils down to this -- is it really AH put through the battery which uses it up, or do the "turns" count, too? So if you short cycle a battery 5 times between 70% and 80%, does that use it up to exactly the same extent as one cycle between 50% and 100%? Or do the four extra "turns" add to the using-up of the battery?

Inquiring minds want to know!
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Old 01-06-2018, 05:09   #9
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Re: What count as a cycle (battery life)

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Originally Posted by gauvins View Post
Thanks for your input.

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

How do you figure this?



It depends a lot on what batteries you choose. Deep cycle flooded batteries can easily outlast many AGM batteries and vice versa it just depends upon what brand, model & type battery you choose.



For example if you chose East Penn / Deka as the manufacturer they rate lab cycle life like this:


12V Flooded Dual Purpose 200 Cycles (Automotive case style batteries G 24,27,31 etc.)


12V Flooded Deep Cycle 350 Cycles (Automotive case style batteries G 24,27,31 etc.)


12V & 6V Flooded Deep Cycle 700-1000 Cycles (Golf Car Type)


12V AGM 300 Cycles


12V GEL 1000 Cycles
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Old 01-06-2018, 05:48   #10
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Re: What count as a cycle (battery life)

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And MaineSail -- you didn't really answer the question, I think -- sure the makers DEFINE cycles like you say, but what is it that uses batteries up? Do you agree with Stu?

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..
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Old 01-06-2018, 05:54   #11
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Re: What count as a cycle (battery life)

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Expected life of a battery is typically expressed in cycles. Say 200 for lead, 600 for AGM, 1000 for lithium.
Where do you get these numbers? AFAIK, quality deep cycle flooded lead acid and quality AGM batteries are both good to 1000 to 1200 cycles @ 50% DOD, whereas LiFePo4's are good for thousands of cycles.

Rated cycle life varies a lot from battery to battery. Trojan T105 golf cart batteries, popular with cruisers, are rated at 1200 cycles @ 50% DOD -- the same as Trojan's AGM batteries.

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Quote:
Originally Posted by gauvins View Post
All I could find were examples of cycles going from full charge to the suggested minimum for a given chemistry. Say 50% for deep discharge, 20% for AGM, 0% for lithium. (I know that one should avoid getting even close to these values in order to optimize battery lives, but I have no idea about the relationship between usual depth of discharge and life expectancy (expressed in total Ah stored and pulled from a battery)
Again -- where do you get the numbers? I don't think there's any difference between deep cycle flooded LA and AGM's in this respect; and you cannot for sure discharge LiFePos to 0% without destroying them. I think about 10% is the lowest you want to go.

I believe that the cost per AH stored and used will be quite a bit less for deep cycle flooded batteries, than for AGM's -- probably less than half. I think you really can't beat 6v flooded golf cart batteries in this regard, especially the Costco (or is it Sam's?) ones which are popular with cruisers. If I had room for them on my boat I probably wouldn't be looking at lithium.

It's commonly said that you shouldn't discharge lead-acid batteries below 50%, but if you look at the DOD vs cycle life charts, I think it's hard to discern any reason why not. Cycle life does not fall off a cliff, but declines proportionately all the way to 20% or so (80% DOD). I realize this contradicts what Stu said about 40% and maybe I'm missing something, but it sure looks to me, from reading all those charts, that you will be using your batteries more economically, especially if you are charging with a generator, if you discharge them further than 50%
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Old 01-06-2018, 06:24   #12
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What count as a cycle (battery life)

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It's commonly said that you shouldn't discharge lead-acid batteries below 50%, but if you look at the DOD vs cycle life charts, I think it's hard to discern any reason why not. Cycle life does not fall off a cliff, but declines proportionately all the way to 20% or so (80% DOD). I realize this contradicts what Stu said about 40% and maybe I'm missing something, but it sure looks to me, from reading all those charts, that you will be using your batteries more economically, especially if you are charging with a generator, if you discharge them further than 50%


What your missing is these charts are extrapolated from lab conditions, which among other things have the bank properly charged completely back to a full 100% each cycle, something that rarely happens on a cruising boat. The deeper you discharge, the longer the charge back to full takes, and very few cruising boats get back to full when discharged to 50%, take them even deeper and you pretty much guarantee they arenít getting back to fully charged.
Cruising boats only have X time to recharge, most do not extend that time to fully charge as it is, they certainly are not if discharged deeply.

Iím pretty anal about this and with my 1 kilowatt of panels it still takes a couple of hours early on the morning to get to 100% SOC and that is from a starting average of 80% or so.
Also Iím throwing 185 amps into a 660 AH AGM bank, most canít do that, but the lab that these charts are based on can throw whatever the bank can handle, they have infinite abilities.

The charts are based on conditions unobtainable on most cruising boats

Iíd suspect a discharge to 20% would take several hours of generator charge, plus panels to get back to full, and I donít see people doing that.

Many people here think there must be something wrong with my panels, but there isnít, itís not their output that is the issue, itís the amount of time they have to charge vs time required to get to 100%. Having extra big Solar array isnít about more amps so much as itís about extending the length of your Solar day.

Most probably people who think their bank is full by noon on panels alone, are not, but you canít convince them of that. The charger drops in to float, they are full.

On edit, how deep you discharge ( to an extent ) isnít as relevant to cycle life as being fully 100% recharged is, they deeper they are discharged, the less likely they are to be fully recharged.
Be interesting to know recharge time to 100% from 20% with the average cruising boats charge source, not an unlimited one.
Yes, I know the bank acceptances rate is much higher at low SOCís but most are limited to 60 amp charges, often less.
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Old 01-06-2018, 06:49   #13
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Re: What count as a cycle (battery life)

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What your missing is these charts are extrapolated from lab conditions, which among other things have the bank properly charged completely back to a full 100% each cycle, something that rarely happens on a cruising boat. The deeper you discharge, the longer the charge back to full takes, and very few cruising boats get back to full when discharged to 50%, take them even deeper and you pretty much guarantee they arenít getting back to fully charged.
Cruising boats only have X time to recharge, most do not extend that time to fully charge as it is, they certainly are not if discharged deeply.

Iím pretty anal about this and with my 1 kilowatt of panels it still takes a couple of hours early on the morning to get to 100% SOC and that is from a starting average of 80% or so.
Also Iím throwing 185 amps into a 660 AH AGM bank, most canít do that, but the lab that these charts are based on can throw whatever the bank can handle, they have infinite abilities.

The charts are based on conditions unobtainable on most cruising boats

Iíd suspect a discharge to 20% would take several hours of generator charge, plus panels to get back to full, and I donít see people doing that.

Many people here think there must be something wrong with my panels, but there isnít, itís not their output that is the issue, itís the amount of time they have to charge vs time required to get to 100%. Having extra big Solar array isnít about more amps so much as itís about extending the length of your Solar day.

Most probably people who think their bank is full by noon on panels alone, are not, but you canít convince them of that. The charger drops in to float, they are full.

On edit, how deep you discharge ( to an extent ) isnít as relevant to cycle life as being fully 100% recharged is, they deeper they are discharged, the less likely they are to be fully recharged.
Be interesting to know recharge time to 100% from 20% with the average cruising boats charge source, not an unlimited one.
Yes, I know the bank acceptances rate is much higher at low SOCís but most are limited to 60 amp charges, often less.
OK, I think that makes a lot of sense.

However, I don't think that discharging to 40% or 30% necessarily correlates to failing to get the battery back up to 100%. On the contrary, it would seem to me that cycling less often but more fully COULD be more conducive to getting those 100% charges in.

OR for some people, like me probably, how deep the bank is charged simply has nothing to do with how often you get up to 100%.

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.

Like many, I cycle between 50% or 60% SOC and 80% or 90%. And then I try to be sure to get in a good full 100% overnight charge at least once or twice a week, one way or another, mostly by going into a harbor (sometimes specially for this purpose), or doing a good long motor passage.

Getting the batts up to 100% more often than this would be such a PITA that you would gladly replace the batteries a little more often in order to avoid it.

But I have been gradually talked into the idea that making it a rigid rule to never ever let the batts get below 50% is wrong-headed.

I think the REAL value of that "rule" may be to deal with wrong data about SOC which people have from their amp-counting battery monitors.

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.

At anchor there isn't really any reason to do this, because I use the generator a couple of times a day ANYWAY for other purposes. I try not to obsess about my batteries - there are enough other things to worry about, and batteries are consumables after all. But with the usual regime of generator use at anchor the batteries are usually kept above 60% anyway. Actually I don't think my boat was designed to be lived in on batteries for long periods of time -- originally she had only 220 amp/hours (@24v) of house batteries (and an equal size bank for winches, windlass, and thruster, but I have now combined them into one) -- I think the designer intended that the heavy duty prime power (continuous duty) rated generator would be on most of the time.

And in fact I don't mind running the generator -- it runs at 1500 RPM and is almost inaudible, so I routinely just crank it up around dinner time when different electric-intensive tasks are being done, or to run a load of laundry, or whatever. The batteries are worked much less hard in this regime where anyway the generator is on a few hours every day.
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Old 01-06-2018, 07:36   #14
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Re: What count as a cycle (battery life)

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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.
I am rather pleased you have said this as I was struggling to compare different batteries and types. The price of these in the UK is £159 which is comparable to a good quality 12v FLA, but has 4 x the cycles, too good to be true perhaps?

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Old 01-06-2018, 07:44   #15
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What count as a cycle (battery life)

Whether you realize it or not, your close to a powerboater way of thinking.
Nothing wrong with that, itís just a different way of doing things is all.
Back in my Sportfishing days, the generator came on before we unplugged from the dock, and stayed on until we plugged back in.
We never anchored out, could have, but why when the dock was right there, and besides that is where the Motel room with a shower and bar was.
Iím not saying that is you , but itís a different world when your anchored for long times and Solar is your prime power supply. Your vacationing and going places. Most cruisers sit, more than they go.
Your not living aboard at anchor, and that is the difference.
When you do, and your on a reduced Retirement income, then you start thinking 4 hours of generator a day, that is 1,500 hours a year, or a new generator every 4 years or so, a generator costs a couple of grand a year, likely more?
Battery bank is a couple of grand for Lifeline AGM, short cycling them you get a new bank every other year, battery cost another grand a year.

Run Solar heavy and take care of your bank and reduce generator run time and you reduce costs up to three grand a year. $200+ a month is significant to a lot of cruisers, and Iím ignoring fuel.

A lot less of course if you work during most weeks and part time on the Boat, and honestly when I was working of course a couple of extra grand a year was peanuts, stupid cell phone costs more than that
But you spend Iíd guess maybe 50 days a year on the boat, more if your lucky? So in your case it doesnít make sense to go Solar heavy, and baby a bank, worry about generator run time etc. besides your vacationing, recharging from work, why not do it the most enjoyable way?

Iím ruined now, I would not want to go back to work, and neither does the Wife. I thought she would miss it, but doesnít seem to.
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