Comparing battery types

[Rossland]

Batteries: GEL, AGM or Lithium which one is the best? – STEPSOVER

This is an interesting essay comparing various battery technologies. The author is on a RV, but the data here is applicable to boats too. It was originally written in Italian, and the English translation is difficult to read in places. If you can read Italian, you might find the original version easier to understand.

 

[ranger58sb]

Interesting "Expedition RV". Seems like the inside has windows, but the outside doesn't show many.

-Chris

 

[DavidM]

I read the article and it does have some take aways for us boaters. It also had some omissions and some mis-statements.

The important take away was to use a battery monitor to determine your DC watt hour requirements. Reading the data on the appliances nameplate is only a small part of the story. The fridge used 1/5 of the nameplate wattage in a 24 hour period.


Another point made, although it was difficult to follow, was the cost/benefit analysis. According to the article, Li batteries cost 7 times (2,800 vs 400 Eu) Gel/AGM batteries. They do give more than twice the usable capacity though (80% discharge vs 30% discharge). Presumably that is why they chose Gels, although I believe that Gels are becoming less and less available in our markets.


The significant misstatement was that AGM/Gels can only be discharged 30%. Most references indicate 50%. Also the whole subject of discharge/recharge cycle life is suspect for all battery types in my opinion. The only real data I ever saw on this subject was from Trojan and gave battery life vs number of cycles. You can discharge 80% but life is cut dramatically. 50% seems to be the best compromise. Also, and this is my own opinion, 3-4 deep discharges with the rest being at 50% or less, won't significantly affect battery life, as long as they are fully recharged soon thereafter.

The significant omission was FLA deep cycle, ie GC batteries. They have similar operating characteristics as AGMs and cost at least half. The other omission and maybe I missed it, was how do you recharge that huge bank of batteries.

Finally, I was surprised that the fridge and maybe the stove ran on DC (through an inverter maybe) . Propane is used for that on almost all RVs and as a result they typically use a fraction of the DC AHs as boats.

David

 

[Bacchus]

"Finally, I was surprised that the fridge and maybe the stove ran on DC (through an inverter maybe) . Propane is used for that on almost all RVs and as a result they typically use a fraction of the DC AHs as boats."

David.
Many newer Class A MHs are going all electric... especially the diesel pushers. Fridges... many residential are run off inverters and heat & hot water via shore power, gennie or diesel burner.
My 2013 MH has 8 GC house bank. Stove is elec and needs shore power or gennie. No propane frees up one storage bay but batty banks are larger so somewhat of a wash.

 

[DavidM]

Don:


I didn't realize that. My RV is several steps below a diesel pusher- a 20' camping trailer ;-).



So diesel pushers with no propane on board must have diesel generators and diesel fueled furnaces and hot water heaters, although the latter two could be A/C powered from the genset.


David

 

[Rossland]

I read the article and it does have some take aways for us boaters. It also had some omissions and some mis-statements.

The important take away was to use a battery monitor to determine your DC watt hour requirements. Reading the data on the appliances nameplate is only a small part of the story. The fridge used 1/5 of the nameplate wattage in a 24 hour period.


Another point made, although it was difficult to follow, was the cost/benefit analysis. According to the article, Li batteries cost 7 times (2,800 vs 400 Eu) Gel/AGM batteries. They do give more than twice the usable capacity though (80% discharge vs 30% discharge). Presumably that is why they chose Gels, although I believe that Gels are becoming less and less available in our markets.


The significant misstatement was that AGM/Gels can only be discharged 30%. Most references indicate 50%. Also the whole subject of discharge/recharge cycle life is suspect for all battery types in my opinion. The only real data I ever saw on this subject was from Trojan and gave battery life vs number of cycles. You can discharge 80% but life is cut dramatically. 50% seems to be the best compromise. Also, and this is my own opinion, 3-4 deep discharges with the rest being at 50% or less, won't significantly affect battery life, as long as they are fully recharged soon thereafter.

The significant omission was FLA deep cycle, ie GC batteries. They have similar operating characteristics as AGMs and cost at least half. The other omission and maybe I missed it, was how do you recharge that huge bank of batteries.

Finally, I was surprised that the fridge and maybe the stove ran on DC (through an inverter maybe) . Propane is used for that on almost all RVs and as a result they typically use a fraction of the DC AHs as boats.

David

Although he doesn't do a good job of explaining it (at least in the English version), the 30% discharge comes from the fact that gel/AGM batteries accept a charge much more slowly for the last 20% charge. Therefor it is probably not economical to run a generator only to charge batteries from 80% to 100% charge. Gel/AGM batteries should not be discharged below 50%, so the difference is 30%. On our boat, we shut the generator down when the batteries reach 80% charge, unless the generator is also powering something else.

In North America, golf cart or lift truck batteries, may be an option, and the prices quoted for other battery types will be different as well, but the principal is still valid. Anyone planning to replace their battery bank should recalculate using local prices.

And to answer your question about inverters, yes, there is a Victron Quatro and he is planning to add a Victron Multiplus as well.

 

[Bacchus]

Don:


So diesel pushers with no propane on board must have diesel generators and diesel fueled furnaces and hot water heaters, although the latter two could be A/C powered from the genset.


David

Yes... Actually its usually a combined unit w one burner and 1 or 2 elec elements that can supply hot water and hot water heat either via in floor tubing and/or small registers w fans on separate zone T stats.
Additionally when running engine heat can be utilized to provide any of the above. And w an optional pump the furnace can be used for engine preheat in very cold Wx.
Usually AC is also reversable w heat pumps so lots of different ways to satisfy needs depending on temps and power available.
Having a residential multi door / drawer fridge freezer is a huge improvement.

We will be in your neck of the FL woods (Port Charlotte) w our MH in March. If you would like a tour I'll provide the refreshments

 

[FF]

"the 30% discharge comes from the fact that gel/AGM batteries accept a charge much more slowly for the last 20% charge. Therefor it is probably not economical to run a generator only to charge batteries from 80% to 100% charge."

This is to my thinking correct.

The batts will loose capacity over time from not getting to 100% SOC after a discharge.

An equalizing cycle doesn't help much and de sulfators work but can not be on constantly , they too have a current draw..

The usual cruiser solution is to oversize the house bank so 30% in daily use is enough to maintain your std of living after the batts age.

As always almost any solar is a big help, not to attempt to operate everything , just to fill the last 10% or 20% the batts need to be fully charged.

 

[dhays]

Gel/AGM batteries should not be discharged below 50%, so the difference is 30%. On our boat, we shut the generator down when the batteries reach 80% charge, unless the generator is also powering something else.

This is a bit of a digression but... we hear a lot not to go above 50% DOD. I think this is significantly overstated.

My ignorant impression is that any battery will have a limited lifespan that can be described as recharge cycles. Lifeline has a nice graph for their AGM batteries that shows the number of cycles by the depth of discharge.

The Lifeline graph gives these recharge cycles for these depth of discharge.
30%. 1850
50%. 1000
70%. 675

So, lets say that your typical electrical usage is 200Ah between recharges. The deeper the discharge, the small the battery bank to provide those 200Ah.
30% 666Ah
50%. 400Ah
70%. 285Ah

So, obviously the deeper the DOD the shorter the lifespan of the battery bank. OTOH, the deeper the DOD the smaller that battery bank has to be. So, why should you not go below 50% DOD? Let’s compare the cost difference between 30%, 50%, and 70% DOD.

The rough cost of a Lifeline 8D is about $700 and will give 255Ah. This is roughly $2.75 per Ah. Using this, some quick math gives tells us that the cost per recharge cycle at various DOD for that 200Ah demand is;
30% DOD $0.99
50% DOD $1.10
70% DOD. $1.16

So why not go deeper than 50% DOD? Going to 70% DOD instead of 50% will cost you and extra 6 cents per recharge cycle. I try to keep my DOD to only 30% and usually keep it to 20%. So I save 11 cents per cycle. Actually I save close to 20 cents per cycle since my bank is about 780Ah.

Anyway, what is magic about 50%? Why not say not go below 40% instead or go down to 60% DOD?

 

[BruceK]

... the 30% discharge comes from the fact that gel/AGM batteries accept a charge much more slowly for the last 20% charge. Therefor it is probably not economical to run a generator only to charge batteries from 80% to 100% charge....

How does slow recharge of the last 20% in gel/AGM affect the level to which discharge is permissible?
I`ve an interest in replacing FLAs with AGM next time, and wonder if that slow last 20%,which I always thought applied to LAs anyway,is even slower in AGMs. I have solar which ultimately gives me the 100% charge, so I can and do get to full charge.
I thought an advantage of AGMs is they accept charge faster than FLAs. Is that so?

 

[twistedtree]

This is a bit of a digression but... we hear a lot not to go above 50% DOD. I think this is significantly overstated.

My ignorant impression is that any battery will have a limited lifespan that can be described as recharge cycles. Lifeline has a nice graph for their AGM batteries that shows the number of cycles by the depth of discharge.

The Lifeline graph gives these recharge cycles for these depth of discharge.
30%. 1850
50%. 1000
70%. 675

So, lets say that your typical electrical usage is 200Ah between recharges. The deeper the discharge, the small the battery bank to provide those 200Ah.
30% 666Ah
50%. 400Ah
70%. 285Ah

So, obviously the deeper the DOD the shorter the lifespan of the battery bank. OTOH, the deeper the DOD the smaller that battery bank has to be. So, why should you not go below 50% DOD? Let’s compare the cost difference between 30%, 50%, and 70% DOD.

The rough cost of a Lifeline 8D is about $700 and will give 255Ah. This is roughly $2.75 per Ah. Using this, some quick math gives tells us that the cost per recharge cycle at various DOD for that 200Ah demand is;
30% DOD $0.99
50% DOD $1.10
70% DOD. $1.16

So why not go deeper than 50% DOD? Going to 70% DOD instead of 50% will cost you and extra 6 cents per recharge cycle. I try to keep my DOD to only 30% and usually keep it to 20%. So I save 11 cents per cycle. Actually I save close to 20 cents per cycle since my bank is about 780Ah.

Anyway, what is magic about 50%? Why not say not go below 40% instead or go down to 60% DOD?

Exactly!!


There is really nothing magic about 50% DOD as a limit. You can really pick any DOD/lifetime-cycles operating point you want. You cen spend less on batteries and wear them out faster, or spend more and wear them out slower. Your cost over time will be roughly the same either way.


Other considerations:


- If you buy smaller batteries knowing they will need to be replaced sooner, you also have less opportunity to wreck them yourself through miss-use. Many batteries dies because of miss-use, not because they have really been used up. The less time you own them, the less opportunity to do damage, and the smaller bank you have damaged when you do mess up.


- Time value of money favors spending less today on a smaller bank and wearing it out sooner, vs spending more today and wearing it out later.


- And on the flip side, replacing a battery bank is a pain is the butt, so the less often you have to do it, the better.

 

[Rossland]

How does slow recharge of the last 20% in gel/AGM affect the level to which discharge is permissible?
I`ve an interest in replacing FLAs with AGM next time, and wonder if that slow last 20%,which I always thought applied to LAs anyway,is even slower in AGMs. I have solar which ultimately gives me the 100% charge, so I can and do get to full charge.
I thought an advantage of AGMs is they accept charge faster than FLAs. Is that so?

I was referring to charging batteries from a generator, and at what point does the charge acceptance rate slow so much that it is no longer economical to continue running the generator. On our boat, this point is at approx 80% battery charge. Of course, when charging from other sources, shore power, PV array, propulsion engine alternator, the batteries will reach 100% charge, but it will take a few hours to do the last 20%. AGM batteries do accept a charge faster than flooded, but the charge acceptance rate still tapers.

Charge acceptance rate tapering as charge approaches full is a characteristic of lead based batteries, flooded, AGM, GEL. Lithium batteries will accept a charge at the full rate until they are at nearly 100%.

 

[sunchaser]

Good points TT and DH. We're on our 3rd set of FLAs since the vessel was new. I consider them like disposable razors. Monitor carefully and throw away before I get nicked.

Also, am I an outlier? Never had a problem getting near 100% SOC on a daily basis when cruising. Eschewing big reefers may be the reason.

 

[ranger58sb]

This is a bit of a digression but... we hear a lot not to go above 50% DOD. I think this is significantly overstated.

My ignorant impression is that any battery will have a limited lifespan that can be described as recharge cycles. Lifeline has a nice graph for their AGM batteries that shows the number of cycles by the depth of discharge.

So why not go deeper than 50% DOD? Going to 70% DOD instead of 50% will cost you and extra 6 cents per recharge cycle. I try to keep my DOD to only 30% and usually keep it to 20%. So I save 11 cents per cycle. Actually I save close to 20 cents per cycle since my bank is about 780Ah.

Anyway, what is magic about 50%? Why not say not go below 40% instead or go down to 60% DOD?

There was a big discussion on cruisersforum about exactly that. The thread title has the word "myth" in it. After about the first 300 responses, some factoids began to creep in... and there some significant pi$$ing match going on in there too...

The extremely short version is that 50% is only a rule-of-thumb, YMMV, and it kind of represents a balance between getting fair use from your batteries and murdering them.

-Chris

 

[dhays]

Other considerations:


- If you buy smaller batteries knowing they will need to be replaced sooner, you also have less opportunity to wreck them yourself through miss-use. Many batteries dies because of miss-use, not because they have really been used up. The less time you own them, the less opportunity to do damage, and the smaller bank you have damaged when you do mess up.


- Time value of money favors spending less today on a smaller bank and wearing it out sooner, vs spending more today and wearing it out later.


- And on the flip side, replacing a battery bank is a pain is the butt, so the less often you have to do it, the better.

Great points Twisted. A couple more considerations...

- Comparing 70% DOD to 30%DOD. If you have to replace 200Ah into the bank, I believe (electric folks please check me on this) that it will take quite a bit less time to fully replace that 200Ah in a small bank vs a large bank. In a small bank, much more of that 200Ah will be replaced in the bulk phase which replaces the power so much faster. In my bank at 20% DOD, the charger spends almost no time in bulk phase.

- Despite the valid time value of money argument you mentioned, the other consideration is that the cost of batteries is going up. A large bank might amortize to $1.00 per charge over 10 years vs $1.15 per charge over 5 years. How much more will the batteries cost in 5 years?

 

[DavidM]

I have followed the arguments for accepting lower discharge levels with smaller batteries and there is some validity to that argument.


But I prefer to have the largest bank that is reasonably possible for two reasons: to have plenty of capacity for long anchorages with no sun, and to put amp hours in faster with the propulsion engine when I cruise to the next anchorage. The downside to the latter is that it leaves the batteries with a lot of unfilled capacity if you don't cruise long enough to the next anchorage.


I have cruised long term with 1) no solar and only a high output propulsion engine alternator, 2) genset, high output alternator and no solar 3) 200 watts of solar and high output alternator and 4) small solar, genset.


It is all a compromise and all can usually be made to work.



David

 

[CMS]

This is a bit of a digression but... we hear a lot not to go above 50% DOD. I think this is significantly overstated.

My ignorant impression is that any battery will have a limited lifespan that can be described as recharge cycles. Lifeline has a nice graph for their AGM batteries that shows the number of cycles by the depth of discharge.

The Lifeline graph gives these recharge cycles for these depth of discharge.
30%. 1850
50%. 1000
70%. 675

So, lets say that your typical electrical usage is 200Ah between recharges. The deeper the discharge, the small the battery bank to provide those 200Ah.
30% 666Ah
50%. 400Ah
70%. 285Ah

So, obviously the deeper the DOD the shorter the lifespan of the battery bank. OTOH, the deeper the DOD the smaller that battery bank has to be. So, why should you not go below 50% DOD? Let’s compare the cost difference between 30%, 50%, and 70% DOD.

The rough cost of a Lifeline 8D is about $700 and will give 255Ah. This is roughly $2.75 per Ah. Using this, some quick math gives tells us that the cost per recharge cycle at various DOD for that 200Ah demand is;
30% DOD $0.99
50% DOD $1.10
70% DOD. $1.16

So why not go deeper than 50% DOD? Going to 70% DOD instead of 50% will cost you and extra 6 cents per recharge cycle. I try to keep my DOD to only 30% and usually keep it to 20%. So I save 11 cents per cycle. Actually I save close to 20 cents per cycle since my bank is about 780Ah.

Anyway, what is magic about 50%? Why not say not go below 40% instead or go down to 60% DOD?

Unfortunately none of this data applies or translates accurately to the real world. This is why Lifeline specifically states the depth of discharge should be "no greater than 50%". They do this because when they initially launched into the marine, RV and off grid market they did advise 80% DOD. It is how they made their cost comparisons work against flooded lead acid.. As one who's been there & done that, and got the arrows in my back as an early AGM pioneer, I will strongly suggest you do not do this.

Because our shop is running actual 20 hour capacity tests of batteries, on a near continual daily basis, I do get a good chuckle out of manufacturers cycle life claims vs. DOD charts. They are nothing more than complete fairy tales when you try to translate them to real world use....

Those cycle life vs. DOD graphs are mathematically derived based on white-glove "laboratory" cycling at a particular DOD then all other points are extrapolated.. This is why the energy throughput numbers appear to come so close and would appear or suggest that a smaller bank, cycling deeper, will save you money. I would LOVE to tell you that you can do this successfully, as there are many benefits to deep cycling beyond 50%, but it fails miserably outside of a lab and mathematically calculated data that can't predict for real world scenarios....

The point that I agree on is that 50% is not a magic number. Cycle shallower and the bank will last even longer. The occasional cycle to 80% DOD, when necessary, is not going to install kill the bank either but it should be followed up ASAP with a 100% SOC recharge. I have off shore race boats that do cycle AGM's to 80% DOD, due to weight & and energy input needs, but those batteries are almost always replaced yearly, and need to be.

Regularly cycle to 80% DOD in the real world and the life of the battery can be measured in months, not years. The total energy throughput at 80% DOD vs. 50% DOD does not follow the charts, at all.

The only lead acid battery I know of, that can routinely survive regular cycling to 80% DOD is the Firefly Carbon Foam AGM.

 

[twistedtree]

And of course the cat's meow (what an odd expression that is) are LFP batteries. There I think you actually can get away with a smaller bank, partly because you can more deeply cycle them, but more so because you can quickly charge them back up without the endless absorb cycle. My feeling is so what if the generator runs more frequently. The total run hours will still be less than with AGMs because all the charge time is actual, effective charging. Although it would be nice to avoid, I could probably deal just fine with an automatic 2 hr gen run in the middle of the night.

 

[dhays]

Thanks Rod. Your real world experience and knowledge is really valuable. My bank is sized such that most nights I don’t go below 20% DOD so I’ve definitely gone for the larger side rather than smaller and deeper DOD.

 

[BruceK]

...How much more will the batteries cost in 5 years?

On what I see here AGMs are coming down in price,almost the same as FLAs. Admittedly they are from China. I think we have to accept they can and usually do produce acceptable quality.

 

[DDW]

A couple of points:

In a charge-challenged world, you would like to use the 50% - 80% range in L.A. batteries as that keeps them away from low charge/short life and also the long charge tail above 80%. This works Ok with flooded cells and is what much of the sailboat crowd (who are always charge-challenged) do. There is a problem with that on AGMs: they must be periodically recharged to 100% or they will lose capacity unrecoverably. If you do not have the means or the time to do this say once a week, stick with flooded. On a powerboat if you move at least once a week, you are probably going to have the 6 hours or so to achieve 100% charge. Carbon foam AGM batteries do not exhibit this problem according to numerous tests, but cost 50% more.

Second point: strictly speaking one must look at lifecycle costs if comparing costs. How many amp hours/dollar will the battery deliver over it's life? And in most analysis, LFP wins this hands down. There is a large initial capital investment, but because of the much higher useable capacity (10% - 90% instead of 50% - 80%) and the much higher cycle life, the cost per AH delivered by end of life is well below any lead acid variation. Also LFP batteries do not suffer from continued operation at partial state of charge as AGM do. They can be charged much faster, which is sometimes an advantage.

That doesn't make it always the right choice for everyone. The technology for charge and management is more complicated, the initial investment is higher, and the life may exceed the life of the boat, owner, or ownership.

 

[twistedtree]

A couple of points:

In a charge-challenged world, you would like to use the 50% - 80% range in L.A. batteries as that keeps them away from low charge/short life and also the long charge tail above 80%. This works Ok with flooded cells and is what much of the sailboat crowd (who are always charge-challenged) do. There is a problem with that on AGMs: they must be periodically recharged to 100% or they will lose capacity unrecoverably. If you do not have the means or the time to do this say once a week, stick with flooded.

I believe this is a characteristic of all lead-acid battery types, flooded and AGM alike. The lead sulfate that forms when discharging, is nominally all recombined on re-charge. But when a battery is left for extended time in a partial state of charge, the lead sulfate crystallizes and becomes much more difficult to recombine. As portions get left behind, battery capacity is lost. Equalizing can recover some of the lead sulfate, depending on how hardened it has become. Both flooded and AGM batteries need to be brought back to full charge on a regular basis to prevent/limit sulfate formation.

 

[North Baltic sea]

Hi,

https://www.practical-sailor.com/issues/37_53/features/Fighting-Sulfation-in-AGMs_11691-1.html

Very good AGM battery article...

NBs

 

[ranger58sb]

Believe that was written by CMS/MaineSail aka RC.

-Chris

 

[catalinajack]

Good points TT and DH. We're on our 3rd set of FLAs since the vessel was new. I consider them like disposable razors. Monitor carefully and throw away before I get nicked.

Also, am I an outlier? Never had a problem getting near 100% SOC on a daily basis when cruising. Eschewing big reefers may be the reason.

I also have no problem reaching 100% after 5 or more hours cruising. Our house bank is 940 AmpHours (nominally). Alternators are 100-amp Balmars derated to 93 Amps. We have two 12-volt reefers, one Engel fridge-freezer running on 120 VAC, and a 5 cubic foot freezer also on 120 VAC and an ice-maker.

 

[AusCan]

Lot of good points raised regarding how batteries are used. What works well for me, wont't necessarily work well for you and vice versa.

The cost of batteries also varies widely in different regions. Here in Australia, quality chinese AGM's are cheap and plentiful. We don't see the low price golf cart batteries like in the US.

Whatever you use for a battery bank, the trick seems to be - Don't undersize it.

For me, it is easy with minimal electric requirements, and multiple charging options. I don't think my AGM batteries have ever dropped below 75%, and they get fully charged by shore power, alternator, and/or solar every day. No generator required. I expect to get 8 or 10 years life out of the batteries.

 

[denverd0n]

The cost of batteries also varies widely in different regions. Here in Australia, quality chinese AGM's are cheap and plentiful. We don't see the low price golf cart batteries like in the US.

Even within the U.S. there is a lot of variation. Golf cart batteries are available quite cheaply all over the place here in Florida. Not so much in a lot of other states.

 

[Delfin]

Perhaps another reason, besides those expressed by CMS, for not deeply discharging Pb batteries of any configuration is the greater voltage drop you see when a load comes on to a discharged LA battery. That plays havoc with some electronics, as I found to my dismay when the 24v PCB on my Kabola boiler crapped out, due to voltage variations, according to the manufacturer, who no longer offers a 24v option for their product since the ALL fail at some point. Admittedly, I think that board was much more sensitive than it should have been....

 

[markajh]

Batteries: GEL, AGM or Lithium which one is the best? – STEPSOVER

This is an interesting essay comparing various battery technologies. The author is on a RV, but the data here is applicable to boats too. It was originally written in Italian, and the English translation is difficult to read in places. If you can read Italian, you might find the original version easier to understand.

AGM is a great battery and the cost has become reasonable. They are also safe and more compatible with old charging systems.

Lithium are of course amazing BUT ka-ching. And whatever you choose, make sure they are compatible with your charging system

 

[Boatfever]

"AGM is a great battery and the cost has become reasonable."

Not sure they're this reasonable - In the middle of buying 8 Trojan 6 volt T145's (260 Ah @ 20hr rate) for $180 each. Shipping isn't final but should be between $100-200.
Looked at Carbon Foam and like what I've found so far but they'll probably be the replacements for these Trojans. Also about to pull the trigger on a Victron Multiplus 3000W


Edit- Also springing for two watering kits at $91each so there's that cost to add to it.