AGM deep cycle vs. AGM solar battery

[Boonie]

The last piece of my solar install is the storage battery. I don't know how to explain my simple understanding, but here goes.

It seems that residential solar systems have been using a different technology in designing their storage batteries than the dual purpose deep cycle batteries we typically use in RVs. We started out needing a single battery that could offer both cold engine starting capacity along with the ability to draw down the battery running appliances/lights (House function). We have moved from a single battery to dual battery set-ups splitting the engine starting function from the house function, but we were still using the deep cycle dual purpose batteries. To gain more storage capacity we started using dual house battery set-ups even going to dual 6-volt golf cart batteries. Since the current draw on an RV solar set-up is closer to our appliance/lights function many RVs are now using the solar designed batteries as their house battery.

If this is true then I do not want a dual purpose deep cycle battery either flooded cell or AGM such as an Optima "color" top. What I am looking at is a VMax SLR125 125 AH. What concerns me is the statement in their literature; "Recommended solar panel 175W-450W (120w may be used if Depth of Discharge does not exceed 50%). Even the VMAX 100 AH; "Recommended solar panel 150w-400w (100w may be used if DoD dose not exceed 50%) Since my initial array will be 120w, I am confused. I do not want to loose the capacity offered by this type of battery or somehow damage it. Is this limitation only on the VMax or is this typical of solar batteries?

So I turn this over to the electrical wizards and solar gods for your insight and recommendations.

PS I have assumed the design standard of a 50% depth of discharge in selecting the 120AH. i.e. 30AH per day, 2 days=60AH/50%=120AH

 

[Vic Harder]

Hey Boonie. Confusion is normal because of all the (mis)information out there. It drove www.HandyBobSolar.com nuts. His rants are right on and well, ranty.

I'm actually pleased to see VMax making suggestions for PV array size. The reason they are making those suggestions is because they want you to be able to fully recharge daily, meaning discharge to 50%, and recover to 100% daily. They are making guesses about how efficient your PV array will be, and use a rule of thumb I have seen elsewhere, that your PV power rating should be about 3x your battery AH rating. 125 AH battery bank = 250W solar array.

Obviously if you are keeping an eye on your battery and get to 55%, you may want to change your situation - either stop using power or go for a drive to charge up the batteries.

Rando will likely point out that 50% is not a do or die level either. I agree. Just don't make a habit of regularly going below 50%.

 

[JaSAn]

Lead acid battery rule of thumb: The more a battery is discharged the more sulfates are deposited on the lead plates. The longer the battery is not fully charged (100%) the harder those sulfates are to get back into solution. This is why it is important to get to 100% as often as possible.
http://batteryuniversity.com/learn/article/lead_based_batteries

A concern for me on the VMax SLR125 battery is that ~5% of the respondents on Amazon say the battery won't hold a charge after a short while, with poor response from the company.

IMO a good battery monitor (like the Trimetric) would be a good investment for any solar charging system.

jim

 

[Boonie]

Vic, thanks. As long as the ability to recharge is the issue and not the actual size of the array (recharge rate) or the depth of discharge. For me that means breaking out the 100w portable to increase my ability to recharge.

Jim, most deep cycle batteries require about five cycles in order to "condition" the battery and achieve the ability to hold a 100% charge. Could it be that the 5% didn't read the manufacturers recommendations for conditioning and thus their poor results? (I'm a man I don't need to read instructions!)

Is 50% depth of discharge the rule of thumb for all types of lead acid batteries no mater whether Dual Purpose deep cycle or Solar deep cycle?

Can someone explain why Dual Purpose deep cycle batteries have high CCA but low AH thus causing dual battery installations while Solar deep cycle can achieve higher AH in a single battery?

 

[smlobx]

To me this is one of the most confusing issues related to truck camping....

If you were going to camp in one place for an extended time ( 3 or more days) then I could see a pure discussion on refresh rate of your solar array etc. coming into play. However, many of us are wanderers and are often driving and exploring the land. In such a case your truck will do a good job of charging your batterie(s) even without any solar panels.

Of course, this is also very dependent on your latitude, time of year etc which will significantly influence the efficiency of your set up.

For us, we have 200 amps of solar and two deep cell 6 volt batteries in our camper. Our truck is a diesel with two batteries and a 220 amp alternator that quickly charges the batteries when driving.

We also use a NOCO smart charger when not camping in order to keep our batteries in the best shape possible..
https://www.amazon.com/NOCO-G7200-UltraSafe-Battery-Charger/dp/B004LWTHP2/ref=sr_1_1?ie=UTF8&qid=1491338405&sr=8-1-spons&keywords=noco+genius+charger&psc=1

 

[Boonie]

To me this is one of the most confusing issues related to truck camping....

If you were going to camp in one place for an extended time ( 3 or more days) then I could see a pure discussion on refresh rate of your solar array etc. coming into play. However, many of us are wanderers and are often driving and exploring the land. In such a case your truck will do a good job of charging your batterie(s) even without any solar panels.
OK, I do both
Of course, this is also very dependent on your latitude, time of year etc which will significantly influence the efficiency of your set up.
Check, I've got that.
For us, we have 200 amps of solar and two deep cell 6 volt batteries in our camper. Our truck is a diesel with two batteries and a 220 amp alternator that quickly charges the batteries when driving.
Why do you use two 6 volt batteries for the camper? What is you AH capacity?
We also use a NOCO smart charger when not camping in order to keep our batteries in the best shape possible..
Got one. Use it at home before I head out or in campgrounds (God forbid) when sun doesn't shine for extended days.

 

[craig333]

What do you drop your batter(ies) to? I've yet to even come close to a 50% discharge. If you don't either then getting it back to 100% is much easier. I've come to think its a misnomer to think batteries like the optima are "deep cycle" battery. It may have some traits but its not a real deep cycle battery. I have the biggest yellow top they make sitting here making a living as door stop. If anyone wants to try and revive it they're welcome.

 

[Casa Escarlata Robles Too]

Last year when I ordered my VMAX 100ah solar AGM I looked at their info about the amount of solar compared to battery size.
I only have 105 w solar but don't park for longer then a day without moving,so I was OK with the size I ordered.
I was going to get a larger one but the 50% rule changed my mind.
100ah is more then enough for our usage.
Frank

 

[JaSAn]

Jim, most deep cycle batteries require about five cycles in order to "condition" the battery and achieve the ability to hold a 100% charge. Could it be that the 5% didn't read the manufacturers recommendations for conditioning and thus their poor results? (I'm a man I don't need to read instructions!)

Is 50% depth of discharge the rule of thumb for all types of lead acid batteries no mater whether Dual Purpose deep cycle or Solar deep cycle?

Can someone explain why Dual Purpose deep cycle batteries have high CCA but low AH thus causing dual battery installations while Solar deep cycle can achieve higher AH in a single battery?

Boonie,

I just wanted to point it out to you, in case you hadn't seen, that some users of that battery were not thrilled. When I see that number of bad reviews it triggers a little more thorough investigation. I have no idea other than what they posted as to why the failure.

Going below 50% damages a battery. You always loose capacity. Charging back to 100% seems to never get rid of all the sulfation on the plates. Increasing from 30% to 50% depth of discharge will kill your batteries twice as fast. It is common for all lead/sulfuric acid batteries.

The site (battery university) I linked to in my first post gives a good explanation of the difference between starter and deep-cycle batteries. Marine or dual purpose batteries are a compromise between the two. If the battery(s) don't weigh ~70 lbs for every 100AH (at 12V) they ain't deep cycle.

. . . However, many of us are wanderers and are often driving and exploring the land. In such a case your truck will do a good job of charging your batterie(s) even without any solar panels.
. . .
For us, we have 200 amps of solar and two deep cell 6 volt batteries in our camper. Our truck is a diesel with two batteries and a 220 amp alternator that quickly charges the batteries when driving.

Big alternators are great for getting a battery back to 80% quickly, but it will take ~ 3 hours to get your battery from 80% to 100% at absorption voltage no matter how many amps are available.

Why do you use two 6 volt batteries for the camper? What is you AH capacity?

I use golf cart batteries (GC2 at 6V, 208AH each) because they are true deep cycle (mine weigh 62 lbs each), they are available anywhere there is a golf course (I got mine at Sam's Club), and they are the cheapest deep cycle I know of (they are ~ $85 each, you need two in series: 12V, 200+AH).

jim

 

[hebegebe]

My diehard group 31 marine battery gave up the ghost at 4 yrs from date of manufacture to the month I am confused as to what to replace it with. I don't feel like it was good value


Sent from my iPhone using Wander The West

 

[Boonie]

Jim,
The third type of battery that Battery University classifies is a stationary (UPS) battery. I am guessing that this is the solar storage type battery that I originally alluded to. Although BU does explain this type of battery, the concept of vibration was mentioned that may make a stationary battery design unsatisfactory for RV use and therefore answers my question about using this type of battery. This leaves me looking for a true deep cycle and not a dual purpose "deep cycle" which as Craig stated are not true deep cycle batteries.
Thanks for the link,
Boonie

Hebegebe,
Marine batteries/deep cycle batteries are not warrantied in months as starting batteries are because their life is based upon the number of deep cycles and the depth of depletion of the cycles. Your usage may be many deep depletions therefore the shorter (than you expected) life. As I learned from Jim above, choosing a larger battery that you deplete to 70% will last longer than a smaller battery that is depleted to 50% doing the same task.

 

[PaulT]

This site has some general descriptions of starting, deep cycle, dual purpose/marine batteries that may be useful for understanding
https://www.solar-electric.com/deep-cycle-battery-faq.html#Starting,%20Marine,%20and%20Deep-Cycle%20Batteries

Click the "Starting, Marine, Deep Cycle?" link for some of the design differences,

Paul

 

[Esus]

Having just spec'ed out and ordered the components for my system, I feel obligated to chime in and mention that LiFePO4 should be high on your consideration list for a battery. It specifically addresses some of your concerns such as the size of the PV array needed to charge a battery to 100%. In a lithium battery, you can charge to less than 100%, use the battery, and not decrease it's life so even if you under spec the PV array and don't drive for a bit besides potentially of running out of juice eventually you aren't hurting the battery. Also, getting from 80% to 100% with a Lithium battery is much, much faster than when charging a traditional lead acid. Tons of other reasons to consider one as well, weight, life expectancy, the list is long...

 

[Squatch]

When I was looking for a battery for my solar system I told thefolks at my local battery place what I wanted and what I was going to use it for. They recommended this.


It a sealed lead acid true deep cycle with heavy plates. This is the style of battery you were describing for home solar systems. It holds a deep charge but isn't much for cold cranking amps. It's been in my camper hooked up to the solar system since last August. So far I've been pleased with the performance.

I was told that kept charged these should last close to 10 years. it was half the price of an AGM.

I've been using Optima Blue tops in my boat for years. They've done well and charge quickly. Though I don't think they will hold as deep a charge as the camper battery.

 

[Boonie]

Paul,
Great site, it was easier for me to understand than Battery University.

Esus,
I looked up LiFePO4 and got motorcycle batteries but not RV. What make/model/rating did you get?

Squatch,
Yup, that is the solar type is was asking about. Pleased to hear you have not had problems with vibration using it in your camper.

 

[Esus]

Esus,
I looked up LiFePO4 and got motorcycle batteries but not RV. What make/model/rating did you get?

Boonie, it took a while and I even considered building my own, but I finally stumbled across a company in Nevada making one with a built in BMS, 100 ah usable, 3 year warranty. Only 29 lbs! I ended up buying it. Taking it out camping this weekend for the first time. https://battlebornbatteries.com/

Let me know if you'd like any other details. I picked one of their engineer's brains for a good half hour on the phone. Or give'm a call, there nice people and quite helpful.

 

[JaSAn]

. . . I feel obligated to chime in and mention that LiFePO4 should be high on your consideration list for a battery.
. . . Tons of other reasons to consider one as well, weight, life expectancy, the list is long...

Boonie, it took a while and I even considered building my own, but I finally stumbled across a company in Nevada making one with a built in BMS, 100 ah usable, 3 year warranty. Only 29 lbs! I ended up buying it. Taking it out camping this weekend for the first time. https://battlebornbatteries.com/

Let me know if you'd like any other details. I picked one of their engineer's brains for a good half hour on the phone. Or give'm a call, there nice people and quite helpful.

Please keep us informed on how this works for you. I looked at LiFePO4 when I was setting up my system 2+ years ago. Huge advantages! Some reasons why I didn't go there:

1. Very few suppliers. If for any reason your battery dies on the road, you're SOL.
2. Nobody knows how long the shelf life of LiFePO4 are. One can get a lot of cycles out of these but how many years will they last? Nobody knows. I expect at least 5 years out of my GC2s.
3. Can't charge under 32ºF. I live in Minnesota. I camp in the winter. I need to charge my batteries when out.

Here is probably more than you want to know about LiFePO4:

http://www.pbase.com/mainecruising/lifepo4_on_boats

jim

 

[baphenatem]

My diehard group 31 marine battery gave up the ghost at 4 yrs from date of manufacture to the month I am confused as to what to replace it with. I don't feel like it was good value


Sent from my iPhone using Wander The West

Crown or Trojan, unless you're going with AGM, in which case Concorde too.

 

[Esus]

Please keep us informed on how this works for you. I looked at LiFePO4 when I was setting up my system 2+ years ago. Huge advantages! Some reasons why I didn't go there:

1. Very few suppliers. If for any reason your battery dies on the road, you're SOL.
2. Nobody knows how long the shelf life of LiFePO4 are. One can get a lot of cycles out of these but how many years will they last? Nobody knows. I expect at least 5 years out of my GC2s.
3. Can't charge under 32ºF. I live in Minnesota. I camp in the winter. I need to charge my batteries when out.

Here is probably more than you want to know about LiFePO4:

http://www.pbase.com/mainecruising/lifepo4_on_boats

jim

Will do! I was pleasantly surprised by the 3 year warranty on battle born solution. That indicated to me that they are confident in both the battery and also the built in BMS preventing one from accidentally harming the battery. I agree there is very little information on the shelf life. I only ever see the expected number of cycles mentioned. That said, hopefully 3000-5000 cycles is under realistic use conditions in which case it would have to last a long time. I will find out eventually!

One of my main concerns was charging in below freezing conditions. I do quite a bit of cold camping myself. The battery's BMS will prevent it from even accepting a charge when temps are in the 20s or lower, but it will still discharge. My thought is that there should be plenty of juice in it to fire up the furnace and warm things up to acceptable charging temps when needed. That's the plan at least. Curious to see how it pans out in practice.

 

[Boonie]

Score sheet:
VMax 100AH .................................1
Dual golf cart 6V 205AH.................1
Solar PG-12V103 FR (100AH?).....1
Lithium 100AH................................1

No consensus, I guess if it works for you, do it.

In sealed lead cell batteries it's the thickness of the lead plates that makes it a true "deep cycle" which means weight. To save weight and gain life cycles (but lose weight in the pocket book) go lithium.