Ready to dry camp. Need 6V AGM battery recommendations

Kevin Means said:

AGMs can be discharged to 50%, but like other deep cycle flooded batteries, they should be fully recharged soon therafter. Deep cycle batteries can survive repeated deep discharges better than "standard" lead/acid batteies, but it will shorten their lives.

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DOD affects cycle life but it impacts total lifespan delivered Ah very little.  Cycles don't run your stuff, amp hours do.  There really is no point in economizing cycle life since it would take a concerted effort to wear out a battery by discharging it even 80% DOD in RV applications.  100% agreement though that restoring the charge soon and keeping them at 100% between cycles is very important for AGM's.

Some say they charge their AGMs with a standard lead/acid battery charger, using standard (non AGM) charging profiles. They claim to have had no overcharging problems,

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I would believe that - because they'll be undercharged.  SLA's require a sustained higher finish voltage to get to 100% and an FLA profile won't provide that.  So you'll be perpetually only restoring ~90% which will lead to early failure.  But probably not quickly enough to make that connection, they'll just go soft and be deemed "bad batteries".

Mark B.
Albuquerque, NM

Mark_K5LXP said:

DOD affects cycle life but it impacts total lifespan delivered Ah very little.  Cycles don't run your stuff, amp hours do.  There really is no point in economizing cycle life since it would take a concerted effort to wear out a battery by discharging it even 80% DOD in RV applications.  100% agreement though that restoring the charge soon and keeping them at 100% between cycles is very important for AGM's......................
Mark B.
Albuquerque, NM

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I am always frustrated by simplistic, quick one line statements.  "DOD affects cycle life but it impacts total lifespan delivered Ah very little."

It would be very helpful if you would give us details like, the expected life span of the batteries you are using in your statement when used for 180 days of the year boondocking, discharging say 75% of those days to 20% SOC (i.e. using 80% of the capacity each day). 

Or maybe you are talking about the occasional dry camper who uses the batteries for 3-4 camping stays a year each from 3 days to 7 days at a time.  Or perhaps the RV'er who stays overnight w/o elect hook ups 3-10 times a year.  The life of these batteries would most likely be several years when dishcharged 80% for these two examples, as long as they were well cared for when not in use.  Also the owners would probably be happy with the life of the batteries. 

Additionally cover the issue on what it takes to recharge a battery bank discharged to 20% SOC back to 100% every day or every other day for 10 days, or 4 weeks straight.  Or even for a 5 day stay, using 80% of the battery (20% SOC) and getting it back to 100% the next day so you can actually use 80% the next day, the day after, etc. 

You just don't take 80% of the capacity out of a battery and get it back to any wheres near 100% with just a couple hours of generator run time.  Or for that matter it would take a really large amount of solar panels to charge a 400AH battery pack back to 100% after taking 320AH out of it in a day of full sun.  Worse yet is if there is haze or light cloudiness.

The devil is in the details which are left out of a very short statement.

AStravelers said:

I am always frustrated by simplistic, quick one line statements.

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Me too, like the one "never run your batteries below 50%".  Unlike the "50% rule" myth, mine is based on data and stands on its own.  Consider that any battery has a finite number of amp hours it can potentially deliver.  Whether you use that up in two, six or eight years depends on how you use it.  If you actually manage to use a battery up before it fails for some other reason, or age, that's as good as it gets.  It really is that simple.

It would be very helpful if you would give us details like, the expected life span of the batteries you are using in your statement when used for 180 days of the year boondocking, discharging say 75% of those days to 20% SOC (i.e. using 80% of the capacity each day).

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Not possible to estimate this without knowing what kind of batteries. But by using battery capacity rather than try and integrate DOD and cycles and extrapolate from there, you can just calculate the amp hours for a given use period and see what percentage of the total life that represents.

Or maybe you are talking about the occasional dry camper

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It doesn't matter, Ah delivered are Ah delivered.  For very light duty applications like these, cycle life doesn't even enter the equation, you'll never come close.  Some other failure mode will determine their end of life.

cover the issue on what it takes to recharge a battery bank discharged to 20% SOC back to 100% every day or every other day for 10 days, or 4 weeks straight.  Or even for a 5 day stay, using 80% of the battery (20% SOC) and getting it back to 100% the next day so you can actually use 80% the next day, the day after, etc.

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Charge profiles are well documented in battery data sheets. The problem isn't knowing what the optimum profile is, it's implementing it. Whether a given user can effectively restore a given charge and how quickly they can do it is a huge variable for sure. No doubt there are some multistage converters and inverter-chargers that accommodate them better than others but odds are very few owners are going to replace major electrical components in their RV's to achieve this, they'll use what they have.  But the DOD doesn't drive that - it's true whether you've discharged *at all*, not just down to 80%.

You just don't take 80% of the capacity out of a battery and get it back to any wheres near 100% with just a couple hours of generator run time.

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100% agreement. The same is true if you take 50% or any other amount though. None of this changes the premise that DOD doesn't significantly impact battery delivered Ah.  You bring up a great point though with the boondocking scenario.  If you're only restoring the bulk portion of the charge once or twice a day you only get the "middle" 60-70% of the battery capacity.  Over an extended period of this use profile there is no doubt it will impact life, which will be highly dependent on how long and how often this is done.  Someone with a use scenario like extended boondocking or full timing where they're hammering their batteries hard every day, their batteries will fail sooner.  They're using up their delivered amp hours along with operating outside an ideal profile. Just like any other machine that gets a lot of use, it will wear out quicker than one that's lightly or intermittently used.  Technically this isn't an issue with DOD, but failure to return to 100% and frequent use.  This is an age-old issue with active solar systems and is just something you have to factor into your application that's part of the cost of doing business to run your stuff.  None of that is mitigated by setting an arbitrary DOD point but might be somewhat by reviewing the charge profile and process, which is another layer of the onion to peel back.

  Or for that matter it would take a really large amount of solar panels to charge a 400AH battery pack back to 100% after taking 320AH out of it in a day of full sun.  Worse yet is if there is haze or light cloudiness.

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Solar is just a different charge source and has it's own separate set of varibles.

The devil is in the details which are left out of a very short statement.

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The devil is in the details but the statement "DOD doesn't significantly impact delivered Ah" stands on its' own.  Back to the point of my original post, when you run the numbers for what are real world applicaton scenarios for RV's, DOD is not the predominant factor for battery life.  Optimizing charge cycles, load leveling, and all the minutia of pack longevity can be mused and debated but one constant is with few exceptions in RV operating you're never going to burn through all the available cycles a deep cycle battery has by running down to 80% DOD nor are you buying anything by setting a higher arbitrary threshold.  The "50% rule" virtually assures you will be inconveniencing yourself through reduced run time, not using capacity you paid for up front and for those that think they're ahead of the game by buying twice as much battery, they're only paying more up front and banking even more capacity that will go to the recycler unused when it's time to replace the pack.

Mark B.
Albuquerque, NM

Mark_K5LXP said:

The devil is in the details but the statement "DOD doesn't significantly impact delivered Ah" stands on its' own.  Back to the point of my original post, when you run the numbers for what are real world applicaton scenarios for RV's, DOD is not the predominant factor for battery life.  Optimizing charge cycles, load leveling, and all the minutia of pack longevity can be mused and debated but one constant is with few exceptions in RV operating you're never going to burn through all the available cycles a deep cycle battery has by running down to 80% DOD nor are you buying anything by setting a higher arbitrary threshold.  The "50% rule" virtually assures you will be inconveniencing yourself through reduced run time, not using capacity you paid for up front and for those that think they're ahead of the game by buying twice as much battery, they're only paying more up front and banking even more capacity that will go to the recycler unused when it's time to replace the pack.

Mark B.
Albuquerque, NM

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I see we agree in a number of areas and disagree in some areas.

Here is a link to a Trojan Battery PDF file showing the number of life cycles for their AGM battery. 
https://www.trojanbattery.com/pdf/TRJN-0255-SOLAR-AGM-Flyer.pdf

Or if you prefer here is a link to the same information on their website:  https://www.trojanbattery.com/solar-agm-2/

It is good to note that the chart shows that their battery if only discharged 20% (i.e. 80% full) it will get 4500 discharge/charge cycles.  However discharge it 80% (20% full) and you only get 1000 cycles. 

I don't have enough detailed data to truly know if someone would get the identical number of AH's in the life of the battery, if you take 2 batteries, one being 80% discharged and the other only 20% discharged.  I do question if the batteries are truly capable of sustaining their rated AH's for the life of the battery if "run hard and put up wet" on a continual basis. 

But then again maybe most RV'ers wouldn't care if they only got 1000 cycles if they only dry camped or boondocked for 5 day or 30 days of a year.  The battery would outlast the life of their use of the RV.  Or they would ruin it by accidentally totally discharging it, or significantly overcharging it.

It is also good to remember that someone designing their system to use 80% of the battery on a daily or almost daily basis will run into problems getting back to the 100% full to start their new cycle for the next day. 

Only getting back to 80% full and now you now longer have the 80% capacity to use.  You are down to only having 60% capacity to use instead of the 80% you planned for your system. 

If I installed 400AH and planned to use 320AH the first day and can only charge the system to only 320AH capacity (80% full), I now only have 256AH and I really need the 320AH for my life style.  OOPS.  Kind of a problem.  2nd, 3rd, 4th day and beyond I am missing lots of AH I had planned on.  What happens if I can't run my generator as long, or if using solar, I have a rainy day or several rainy days.  Now what do I do. 

Bottom line, I guess all the above doesn't matter since for the "life of the battery" I will get the same number of AH in that "life of the battery". 

Yep, the "devil in the details" comes into play.

A few more details:
--  A lead acid battery starts off at 12.6V when fully charged.  However when down to 30% full, the voltage is only about 11.75V. 
--  A battery at only 11.75V or even 12V and now you want to put a heavy load on the battery pack to run the microwave/hair dryer/coffee maker or whatever device or devices which you want to use, you probably have a problem. 
--  Voltage sag.  Put a load of 20%-25% (or even 10%) of the capacity of the battery and the voltage drops.  Inverters are not happy with very low voltage.  For one it stresses the components.  Another there is usually a low voltage cut out that could keep you from powering whatever with the inverter.  Many inverters allow you to set a very low battery voltage cutout but you stress the inverter components even more.

Anyways it is an interesting discussion.  No simple answer or one size fits all. 

 

AStravelers said:

I see we agree in a number of areas and disagree in some areas.

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I see that we agree on most everything.  Not all issues are addressed or defined though since they're situation specific. 

I do question if the batteries are truly capable of sustaining their rated AH's for the life of the battery if "run hard and put up wet" on a continual basis. 

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One has to assume the data sheets are correct at face value.  To prove it wrong would take some fairly involved testing under the equivalent or actual operating conditions.  Generally speaking the closer you operate the batteries per the data sheet the closer result you will get to it, so unless you're operating outside those bounds you assume you'll get close to manufacturer ratings.  To make assumptions gets you into the same boat as the 50% rule.

But then again maybe most RV'ers wouldn't care if they only got 1000 cycles if they only dry camped or boondocked for 5 day or 30 days of a year.

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This is the exact point I'm making.  Even if you figure you'll only get half the life of just 500 cycles, that's still more cycles than most RV'ers will realistically use.  AND, even if you did manage to use them up before they expire you got your money's worth right there.  Hence my comment better to burn out than fade away.  The most cost effective battery you will have is one you've used up before it gives up.  That's something I don't think most casual users know much about.  Batteries have a calendar life and they will go bad eventually no matter how lightly they're used.  The clock starts the moment they're manufactured so if you're not using them, you're losing them.  Time, cycles or trauma, one or all of these take their toll eventually.

Or they would ruin it by accidentally totally discharging it, or significantly overcharging it.

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And this is the "other failure modes" I speak of.  The longer a battery is in service, the greater the chance something "bad" will happen.  Usually once or twice isn't going to do it in, but over time the insults build up and next thing you know they're going flat in the middle of the night or after a period of storage.  That's not a DOD problem but a user/system issue.  But since it seems to happen suddenly folks want to know why their expensive batteries are kaput, then someone tells them or they read on a forum to "never" discharge below 50%, so that's what must've done it in.

It is also good to remember that someone designing their system to use 80% of the battery on a daily or almost daily basis will run into problems getting back to the 100% full to start their new cycle for the next day. 

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Agreed.  So that becomes a system consideration - how much capacity does one realistically expect from the pack and size it accordingly.  So the 80% isn't necessarily daily but available when needed. 

What happens if I can't run my generator as long, or if using solar, I have a rainy day or several rainy days.  Now what do I do. 

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You run out of power.  There's only so many contingencies you can anticipate.  To design for the boundary conditions adds a lot of complication and cost.  If this was to operate your heart-lung machine it's one thing, but if you have to skip watching TV so you have heat tonight, it's just a design tradeoff.  The astronauts on Apollo 13 had to shed loads to preserve capacity, it's no different in an RV if necessary.  Whatever operating margin you decide to pick should be based on operating requirements though, not padding for DOD.

--  A battery at only 11.75V or even 12V and now you want to put a heavy load on the battery pack to run the microwave/hair dryer/coffee maker or whatever device or devices which you want to use, you probably have a problem. 

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That's not a  battery problem, but an equipment problem.  Whatever devices/inverters you use should be able to operate over the full terminal voltage range of the battery. 

--  Voltage sag.  Put a load of 20%-25% (or even 10%) of the capacity of the battery and the voltage drops.

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Battery capacities are rated at various draws.  Example, the T105 has 130Ah at 75A draw vs the C20 rating of 220Ah.  That's part of the design choice one makes - anticipating the power needs and sizing the pack based on those draws. 

Many inverters allow you to set a very low battery voltage cutout but you stress the inverter components even more.

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I wouldn't give this much consideration.  It's either rated for the operating range of the batteries, or not.  Now, voltage drop of the cabling is a valid issue and at many dozens or even hundreds of amps, milliohms matter and voltage drop  is battery capacity you can't access.  So minimizing drop to the inverter is important just like minimizing drop in solar systems.

No simple answer or one size fits all. 

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Nope.  What's hard to watch is RV folks are given an unworkable setup from the factory or their dealer and then they struggle with it.  It's a fair guess that most people that own an RV don't want to become an EE just to figure out the batteries.  There is no technical reason why this can't be reduced to the complexity of charging and using a cell phone but here we are discussing Peukert, voltage drops, cycles, charge and discharge rates.  I'm thinking that when lithium reaches a critical cost point these systems will be a whole lot more streamlined and integrated, and batteries will just take care of themselves.  But we're not quite there yet.

Mark B.
Albuquerque, NM

There's another consideration.  How long will you keep the RV?  We've been RVing for about 10 years and are on our 3rd RV.  If you have any plan to update, don't throw money away on expensive batteries.  You're not going to get more money when you sell your RV because you have AGM batteries. 

To anyone planning on upgrading their battery system, adding solar, upgrading chargers:

If you plan your system to primarily look at the total AH's you take out of your battery as Mark_K5LXP advocates and design your system to use 70% to 80% of your battery on a daily basis, you will have very significant problems with your system.

This is my primary reason for replying and discussing the pros and cons with Mark_K5LXP. 

One of the major problems is being able to get the batteries back up to over 95% full on a daily basis or even the 2nd or 3rd day.. 

Do your research and see what it take to get a 100AH battery discharged to 20% full, that is using 80AH of the 100AH possible capacity.  Getting 75AH, much less 80AH back in that battery is not a 2-3 hour project.  Perhaps running the generator for 2 hours first thing in the morning and then have 2-3 times as many watts of solar as AH of battery will get your battery recharged on a nice sunny day. 

For a 1-3 night dry camping stay you should be OK.  However if you find you enjoy dry camping/boondocking you will find your system very inadequate.

Just do your homework. 

AStravelers said:

If you plan your system ... and design your system to use 70% to 80% of your battery on a daily basis, you will have very significant problems with your system.

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Not to dismiss the technical challenges with this because they're certainly there, but you specifically used the words "plan" and "design".  If the system is designed to do this then there's no reason it couldn't be used this way.  But I think your point is that most systems are not set up to, or for some reason cannot provide an adequate charge cycle and then you're right, you can't get there from here.  But that's not a DOD problem, it's a system or end use problem.

Do your research and see what it take to get a 100AH battery discharged to 20% full, that is using 80AH of the 100AH possible capacity.  Getting 75AH, much less 80AH back in that battery is not a 2-3 hour project.

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Correct.  I would add it wouldn't matter if you had a 200Ah battery discharged to 40% SOC - returning those Ah for the larger bank at a lesser DOD is no less a challenge.  So then the elephant in the room isn't DOD, it's the charger capacity and sophistication vs bank size and power availability you're using to replenish whatever pack you have, at whatever DOD you're recovering from.  This isn't a DOD problem, but a system specific one based on the user equipment capability and expectation.  If one decides that the answer is to never take out more than X Ah represented by an SOC based on their battery bank because that's all they can replenish with a 3 hour daily genset run time then that's a user choice/limitation, not a battery DOD problem.  Coming from the other direction, if genset use is limited or the source is solar then that power budget has to be accommodated and certainly battery type and size is part of that, but at the end of the day you can't burn through more Ah than you can replace, irrespective of whatever DOD that represents.

As an aside, it's actually a bit quicker to recover Ah from a deeper DOD because charge efficiency is higher during the bulk phase, and a battery more deeply discharged will be in bulk charge phase longer than one that starts at a higher SOC and switches to absorption mode sooner.  So while it's not ideal to run a battery bank between 20% and 80% SOC continuously, those are mostly bulk mode Ah and are returned the quickest.  This is how I use my RV, I never bother with sitting through an absorption phase until I connect to shore power somewhere.  I have plenty of capacity between 80% to 20% SOC so that's the range I run between when boondocking.  When I can plug in they get a complete cycle, equalize and they're ready to go for the next trip.  I fully acknowledge that this is not the most friendly way to treat a battery but I will come nowhere near using up their expected cycle life anyway, so in about 4 or 5 years when they start to get soft I'll get another set and press on.  For someone full time and off-grid this kind of use model would definitely take it's toll on battery life.  But this is no different than any other active solar system that's at some SOC other than 100% most of the time.  It's not unexpected that a system used harder will wear out quicker.  It's the cost of doing business to run your stuff and a design choice to make when selecting system components for your goals.

Mark B.
Albuquerque, NM

For what it?s worth this is my system

4 - GS100 watt Sunpower Solar Panels
Feeding 4 - 6V Lifeline AGM batteries through a
Morningstar 45 amp MPPT controller with a T5 RM2 remote
The inverter is a Xantrex Freedom Xi 2000 watt pure sine wave type with an internal transfer switch.
A Trimetric TM2025-RV monitor
A Progressive Dynamics Inteli-Power 9200 Power Converter/Charger
Onboard 5500 Watt Onan Genset
A Progressive Dynamics HW50C Electrical Management System

This I installed on a 2013 Sunova 33C in which we Boondock for 5 months on BLM land North of Yuma. I have a dedicated circuit for the Inverter (TV?s,  Satellite receivers and three dedicated plugins). I removed the engine battery to allow the installation of 4 AGM batteries under the step. The engine operates off these batteries.

No problem running crockpot, iron, watching TV for several hours a day. Mind you the solar irradiance here is quite often over 800 watts/m2.
One of my best investments was the Trimetric TM2025 RV monitor, I find it is the only one I use!
I have used this system since 2014.

Mark_K5LXP said:

Nope.  What's hard to watch is RV folks are given an unworkable setup from the factory or their dealer and then they struggle with it.  It's a fair guess that most people that own an RV don't want to become an EE just to figure out the batteries.  There is no technical reason why this can't be reduced to the complexity of charging and using a cell phone but here we are discussing Peukert, voltage drops, cycles, charge and discharge rates.  I'm thinking that when lithium reaches a critical cost point these systems will be a whole lot more streamlined and integrated, and batteries will just take care of themselves.  But we're not quite there yet.

Mark B.
Albuquerque, NM

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this is painfully obvious, judging by the "design" of the electrical systems in both my rv's, it is apparent that a professional EE has never been involved
particularly when it comes to the laughable solar options offered.  the in depth conversation I had when I purchased my ORV suggested that I was an exception to the rule and most people are happy to go with the canned 170 Watt option.. after explaining why this standard option was a joke ( i did mention that their solar expertise appeared to be at the "playskool my first solar panel" level ) coupled with the fact that ORV make RV's SPECIFICALLY for off road/boondocking use, the sales guy was embarrassed  to say the least. the underlying issue was as always, cost.
RV manufacturers really need to wake up and address these issues..

Lithium, well it certainly would be nice to have a canned zero maintenance battery, but sadly the market is in it's infancy, lithium ( LFP ) is
easily damaged and the required control systems to protect joe public is not as economical as it could be, hence the cost of
the 12 V drop in packs. approx $900 for a 100 a/h battery !!!

Posted by: garyb1st
? on: May 22, 2019, 01:20:55 AM ? Insert Quote
There's another consideration.  How long will you keep the RV?  We've been RVing for about 10 years and are on our 3rd RV.  If you have any plan to update, don't throw money away on expensive batteries.  You're not going to get more money when you sell your RV because you have AGM batteries. 

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valid point.. however there are solutions to this, one would be to design a "standard" battery module and merely swap it out.
the second is to just take the existing batteries with you to the next RV.

AJW said:

For what it?s worth this is my system

4 - GS100 watt Sunpower Solar Panels
Feeding 4 - 6V Lifeline AGM batteries through a
Morningstar 45 amp MPPT controller with a T5 RM2 remote
The inverter is a Xantrex Freedom Xi 2000 watt pure sine wave type with an internal transfer switch.
A Trimetric TM2025-RV monitor
A Progressive Dynamics Inteli-Power 9200 Power Converter/Charger
Onboard 5500 Watt Onan Genset
A Progressive Dynamics HW50C Electrical Management System

This I installed on a 2013 Sunova 33C in which we Boondock for 5 months on BLM land North of Yuma. I have a dedicated circuit for the Inverter (TV?s,  Satellite receivers and three dedicated plugins). I removed the engine battery to allow the installation of 4 AGM batteries under the step. The engine operates off these batteries.

No problem running crockpot, iron, watching TV for several hours a day. Mind you the solar irradiance here is quite often over 800 watts/m2.
One of my best investments was the Trimetric TM2025 RV monitor, I find it is the only one I use!
I have used this system since 2014.

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That is a well designed system and seems to work very well in the area you go to.  Ditto on the Trimetric.  I wouldn't be without one. 

For anyone dry camping is areas with less sunlight a couple more panels would be very helpful, i.e. 600 watts or more.  I would also go with 2 residential panels of 300 plus watts if you can find a spot on your roof to put them. 

garyb1st said:

There's another consideration.  How long will you keep the RV?  We've been RVing for about 10 years and are on our 3rd RV.  If you have any plan to update, don't throw money away on expensive batteries.  You're not going to get more money when you sell your RV because you have AGM batteries.

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But then there's us. We've been Motorhoming 26 yrs (32 yrs Rving) and just bought our 4th motorhome.

We put Lifelines in the Camelot. When we sold it they were 8 yrs old and getting to the place where they needed to be replaced - getting about 80% of original capacity.