RV Trip Planning Discussions

Go Back   iRV2 Forums > RV SYSTEMS AND TECHNOLOGIES FORUMS > Going Green
Click Here to Login
Join iRV2 Today

Mission Statement: Supporting thoughtful exchange of knowledge, values and experience among RV enthusiasts.
Reply
 
Thread Tools Search this Thread Display Modes
 
Old 07-30-2020, 08:14 AM   #1
Senior Member
 
Join Date: Oct 2012
Location: Denton, Texas
Posts: 112
Battery Question

Which battery solution provides more storage of power?

1. Two 6 volt AGM with 224 amp hours each, or
2. Two 12 volt lithium batteries with 100 amp hours each.

Appreciate the education.
__________________

__________________
Gary and Karen Allison
Denton, Texas
Redwood 39MB, Ford F-350 Diesel, 4X4 Dually
gcakia is offline   Reply With Quote
Join the #1 RV Forum Today - It's Totally Free!

iRV2.com RV Community - Are you about to start a new improvement on your RV or need some help with some maintenance? Do you need advice on what products to buy? Or maybe you can give others some advice? No matter where you fit in you'll find that iRV2 is a great community to join. Best of all it's totally FREE!

You are currently viewing our boards as a guest so you have limited access to our community. Please take the time to register and you will gain a lot of great new features including; the ability to participate in discussions, network with other RV owners, see fewer ads, upload photographs, create an RV blog, send private messages and so much, much more!

Old 07-30-2020, 08:33 AM   #2
Senior Member
 
Sbrownstein's Avatar
 
Ford Super Duty Owner
Join Date: Dec 2010
Posts: 1,531
Quote:
Originally Posted by gcakia View Post
Which battery solution provides more storage of power?

1. Two 6 volt AGM with 224 amp hours each, or
2. Two 12 volt lithium batteries with 100 amp hours each.

Appreciate the education.
Two 12 volt lithium batteries. While they will have only 200 AH, they can be drawn down to a lower state of charge without damage. The two 6 volt AGMs should only be used for about 134 AH safely.

You do need to make sure your charging systems are compatible with lithium.
__________________

__________________
Scott Brownstein
Palm Island, Florida
2015 Georgetown 335DS
Sbrownstein is offline   Reply With Quote
Old 07-30-2020, 08:41 AM   #3
Senior Member
 
richard5933's Avatar
 
Join Date: May 2019
Posts: 1,349
To add to what Scott said, the two 6-volt batteries will only provide 224 amps @ 12v. When you put 6-volt batteries in series to produce 12v, you add the voltage together but the current (amps) stay the same.

When you add to 12-volt batteries in parallel, you add the current (amps) and the voltage stays the same.

AGM batteries are good for about half their available current output, lithium nearly all the way down. Plus, the lithium will maintain a constant voltage as they discharge while AGM will have a diminishing voltage.
__________________
Richard
1974 GMC 4108 - Custom Coach Conversion
richard5933 is offline   Reply With Quote
Old 07-30-2020, 08:59 AM   #4
Senior Member
 
Winterbagoal's Avatar
 
Join Date: Mar 2017
Location: Sarnialabad, Peoples Republik of Canuckistan
Posts: 1,396
Agree with prior posters. All valid regarding LiFePO4 power availabiltity and configuring them.
Charging lithium with a "non-lithium" capable charger will work fine, if it's got an AGM charge algorithm. LiFePO4 and AGMs have almost identical charge profiles. within the margin of error for most modern 3-5 stage chargers. The better brands of lithium batteries also have very specific safeguards built into them, in their on board BMS, so it's really difficult to do them much harm under normal circumstances. The standard types of lithiums Achilles heel is they don't charge well below freezing (32F/0C) temperatures, but there are some specialized "cold weather chargeable" models available. Relion makes some. I have 2 of them.
The downside for most folks is the price.
__________________
2018 (2017 Sprinter Cab Chassis) Navion24V + 2016 Wrangler JKU (sold @ ????)
2016 Sunstar 26HE, V10, 3V, 6 Speed (sold @ 4600 miles)
2002 Roadtrek C190P (sold @ 315,000kms)
Winterbagoal is offline   Reply With Quote
Old 07-30-2020, 09:20 AM   #5
Senior Member
 
Join Date: Jul 2014
Posts: 22,918
What's not " Safe " about drawing lead acid batteries down to 10% or 20% charge ?

You get more AH from the 2, 6 volt 224 AH in series batteries the two 100 AH batteries. There no magic to that math.

The benefit of lithium batteries is that they have a much higher amount of discharge cycles then lead acid batteries.

In both cases, the depth of discharge determines the amount of cycles.

500 cycles with lead acid batteries down to 10%.

3000 cycles with lithium batteries down to 10%.

Both types of batteries double the amount of discharges if only discharged to 50%.

Lithium will last over 10 years, a great choice if you use them often, and for many years.
twinboat is offline   Reply With Quote
Old 07-30-2020, 10:43 AM   #6
Senior Member
 
Join Date: Sep 2017
Location: Northern California
Posts: 606
Then there's the huge weight advantage of lithium.

I agree mostly with the above posts, but I would add that the AGM though seemingly having more capacity at 224 AH in fact does not. The AGM is fairly lossy so around 10% of that 224 AH (or the watthours it translates to) is lost in heat in the battery. Not so with the lithium. Virtually all of the lithium's energy can be used. This difference looms larger if high current loads are applied to the battery.

Likewise, while charging, a lot of the energy put into an AGM (often approximated as 5% though it can hit 10%) goes into heat, not so with lithium. So, with lithium you need less charging and you get more AH delivered to your loads.

If you are considering solar, the lithium jumps out as the clear winner. Here's why:

With AGM, 100% of the solar energy goes into the battery (or heat in the battery) during the bulk stage. In the absorb stage, the current drops precipitously due to battery chemistry and falls well below what the solar could otherwise deliver. Very roughly (depends on depth of discharge and other factors) a third of your solar capability isn't used when charging an AGM.

In addition, if not enough solar is available to truly top off an AGM, solar will undercharge the AGM and thereby shorten its life. It can take 6-10 hours to top off a 50% discharged AGM so it's likely it won't always be topped off (think short winter days when solar is much lower).*

With lithium, there is only a bulk stage** and the charging current is whatever the solar can deliver until the battery is full. And all of the energy goes into usable AH.

Hence, one needs more more solar with AGM than with lithium, roughly 50% more.

I've got a sketch that shows this, I'll post it if I can find it.

* It's commonly assumed that 85% of AGM recharge occurs in the bulk stage, but tests show it may usually be under 80%. This makes the AGM even less likely to be fully recharged by solar. I'll find the link and post it below.

** some lithium suppliers recommend 15 minutes of absorb stage for their batteries, I think to allow time for cell balancing to complete ... or maybe to get that last 1% into the battery. Neither is critical or needs to occur on each recharge.
__________________
2020 GMC Denali 2500HD Crew 4X4 Gas 6.6L Rockwood 8280WS (30' 5th)
600W solar; 300AH LFP battery, 900W PSW inverter
Coming soon: +400W solar & NovaKool RFU9000 fridge
hclarkx is offline   Reply With Quote
Old 07-30-2020, 10:52 AM   #7
Senior Member
 
Join Date: Sep 2017
Location: Northern California
Posts: 606
Here's the link to some interesting information on charging AGM batteries

https://marinehowto.com/how-fast-can...ry-be-charged/

Here's the rough sketch that shows the unused solar capability when charging a lead-acid battery.

Lower left is the normal charge process. Upper right is the bulk/absorb charging with solar. Notice the unused solar during absorb. Lower right is lithium.

With AGM you need time & energy to get through the bulk and absorb stages. With lithium you only have a bulk stage.

Click image for larger version

Name:	Solar Lead acid vs lithium.jpg
Views:	5
Size:	159.3 KB
ID:	295111
__________________
2020 GMC Denali 2500HD Crew 4X4 Gas 6.6L Rockwood 8280WS (30' 5th)
600W solar; 300AH LFP battery, 900W PSW inverter
Coming soon: +400W solar & NovaKool RFU9000 fridge
hclarkx is offline   Reply With Quote
Old 07-30-2020, 10:53 AM   #8
Senior Member
 
Sbrownstein's Avatar
 
Ford Super Duty Owner
Join Date: Dec 2010
Posts: 1,531
That was my point...regarding "safely". Battery life. I think you probably knew that.
__________________
Scott Brownstein
Palm Island, Florida
2015 Georgetown 335DS
Sbrownstein is offline   Reply With Quote
Old 07-30-2020, 11:03 AM   #9
Senior Member
 
Join Date: Nov 2018
Location: Beaver Dam, Wisconsin
Posts: 1,308
All good advice above even though there appears to be disagreement.

Lithium performs head and shoulders above lead acid. The cost is head and shoulders above lead acid as well, as pointed out above.

How low can you go? There are a few reasons why many people try not to draw their lead acid batteries below 50%. The most frequent reason is they believe it. Functional reasons are subtle and rarely discussed.

Mostly the functional reasons are for optimizing dollars. You can get twice as many discharge cycles drawing down to 50% as you can drawing down to 10%. Of course you need twice as many batteries to provide the same capacity.

Still you get 300 to 400 full discharge cycles drawing down to 10%. For me that is more than 10 years. For a full time boon docker, that may be less than 2 years. I try to recharge sooner so that I have reserve capacity in case things don't go as planned.

Lower output voltage when state of charge is lower can affect inverters. They may trip on low voltage when drawing heavy current. Drawing heavy current greatly decreases voltage until the draw stops. Lower voltage will not affect lights, pumps, etc. much. Some control boards may have trouble while the inverter is drawing high current.

A 400 amp hour battery bank is more efficient delivering 60 amps to the inverter than a 200 amp hour battery bank. Less power is lost internal to the battery. AGM batteries are frequently more efficient charging or discharging at high currents>

Damage to the lead plates can occur when you draw flooded cell lead acid batteries flat. Not so with AGM batteries. Most AGM's tolerate flat discharge without damage. That is do to AGM chemistry and physical design.

Of course there may be other reasons I am not aware of.

I wish you good luck and happy trials ahead!
__________________
Paul Bristol
Kodiak Cub 176RD
Nissan Pathfinder 2015
Persistent is offline   Reply With Quote
Old 07-30-2020, 12:10 PM   #10
Senior Member
 
Join Date: Oct 2012
Location: Denton, Texas
Posts: 112
Thanks everyone! Appreciate the education.
__________________
Gary and Karen Allison
Denton, Texas
Redwood 39MB, Ford F-350 Diesel, 4X4 Dually
gcakia is offline   Reply With Quote
Old 07-30-2020, 12:51 PM   #11
Senior Member
 
Winnebago Owners Club
Workhorse Chassis Owner
Join Date: Nov 2018
Posts: 717
Persistent made all my points quite eloquently except one, and that is system cost. There is a great case to be made for lithium if you need those capabilities, and you're willing to pay for it. For most, running your stuff for a night or two is all that's needed and lead acid is well up to that task and quite economically. If I don't *need* a battery that can go for thousands of cycles and can last a decade or more, then why would I pay the money up front for one? There is a "sweet spot" of performance vs economy that's unique to each application, so applying the landed cost and operational constraints should drive the solution, not necessarily which one is technically "best". "Good enough" can get you there too.

Mark B.
Albuquerque, NM
Mark_K5LXP is offline   Reply With Quote
Old 07-30-2020, 02:24 PM   #12
Senior Member
 
Join Date: Sep 2017
Location: Northern California
Posts: 606
Lots of good info .... I'll add some yet more subtle considerations ........

If you go solar, you will save money on the solar and that will help cover the cost of LFP. This was probably clear from my earlier post. I didn't mention though that charging an AGM with a modest solar system can easily leave it a bit short of fully charged and this takes a bit of extra life out. This is another reason an AGM needs a larger solar array.

If you are a light electrical energy user, for instance expecting to camp a week without re-charging, then the LFP has another advantage ... it can sit indefinitely at lower charge levels without losing measurable life. An AGM, like flooded batteries will have its life shortened if it is not being charged often. AGM is less affected than flooded but still is best re-charged daily. AGM cycle life estimates are usually based on daily re-charging.

A lesser point, AGM batteries are best charged at a relatively high rate (see the article I referenced earlier). As such, the slower charge rate of a modest solar installation, say one that will recharge from 80 to 100% in a day is a bit rough on the AGM but is not a factor in LFP life. In fact, ideally an LFP is charged at a lower rate (stored at 50% state of charge).

Another lesser point, SOC monitoring of an AGM is very approximate because of the losses during charging and discharging which can't be tracked well. A high-end SOC monitor (e.g., Victron BMV-712) will take those into account, but not at all precisely. SOC monitors are only reset or "synchronized" (Victron's terminology) when the AGM is fully charged and because of the difficulty in tracking SOC, that needs to be fairly often. With LFP these internal losses are small so the SOC monitor does not drift as much.

I don't know if anybody mentioned the lighter weight .....
__________________
2020 GMC Denali 2500HD Crew 4X4 Gas 6.6L Rockwood 8280WS (30' 5th)
600W solar; 300AH LFP battery, 900W PSW inverter
Coming soon: +400W solar & NovaKool RFU9000 fridge
hclarkx is offline   Reply With Quote
Old 07-30-2020, 03:17 PM   #13
Senior Member
 
Join Date: Feb 2018
Posts: 798
While the 20 hour discharge rate for the AGMs may be closer to the LiFePO4 batteries in high current inverter usage the LiFiPO4 batteries will be able to sustain close to 100% of the rated output. The life of the Lithiums at 80% discharge may just be about 500 cycles or less while the LiFePO4 batteries may do 3000-5000 cycles at the same discharge rate.

When discharging at a 50-200 amps with an inverter the AGM batteries will have huge voltage sags that will be unable to sustain the discharge rate.

When recharging the AGM will waste much of of the charging energy as heat instead of usable charge.
__________________
Jeff--
Arctic Fox 22G w/1440 watts solar/GMC2500HD Double Cab with Leer Cap w/300 watts solar
astrocamper is offline   Reply With Quote
Old 07-30-2020, 03:54 PM   #14
Senior Member
 
Winterbagoal's Avatar
 
Join Date: Mar 2017
Location: Sarnialabad, Peoples Republik of Canuckistan
Posts: 1,396
Quote:
Originally Posted by hclarkx View Post
Then there's the huge weight advantage of lithium.

I agree mostly with the above posts, but I would add that the AGM though seemingly having more capacity at 224 AH in fact does not. The AGM is fairly lossy so around 10% of that 224 AH (or the watthours it translates to) is lost in heat in the battery. Not so with the lithium. Virtually all of the lithium's energy can be used. This difference looms larger if high current loads are applied to the battery.

Likewise, while charging, a lot of the energy put into an AGM (often approximated as 5% though it can hit 10%) goes into heat, not so with lithium. So, with lithium you need less charging and you get more AH delivered to your loads.

If you are considering solar, the lithium jumps out as the clear winner. Here's why:

With AGM, 100% of the solar energy goes into the battery (or heat in the battery) during the bulk stage. In the absorb stage, the current drops precipitously due to battery chemistry and falls well below what the solar could otherwise deliver. Very roughly (depends on depth of discharge and other factors) a third of your solar capability isn't used when charging an AGM.

In addition, if not enough solar is available to truly top off an AGM, solar will undercharge the AGM and thereby shorten its life. It can take 6-10 hours to top off a 50% discharged AGM so it's likely it won't always be topped off (think short winter days when solar is much lower).*

With lithium, there is only a bulk stage** and the charging current is whatever the solar can deliver until the battery is full. And all of the energy goes into usable AH.

Hence, one needs more more solar with AGM than with lithium, roughly 50% more.

I've got a sketch that shows this, I'll post it if I can find it.

* It's commonly assumed that 85% of AGM recharge occurs in the bulk stage, but tests show it may usually be under 80%. This makes the AGM even less likely to be fully recharged by solar. I'll find the link and post it below.

** some lithium suppliers recommend 15 minutes of absorb stage for their batteries, I think to allow time for cell balancing to complete ... or maybe to get that last 1% into the battery. Neither is critical or needs to occur on each recharge.
Further to the charging info, lithium batteries do not have to be fully recharged to 100% after use, unless they've been drawn to zero SoC. Good point about the weight difference, particularly on some of the OCCC "challenged" models of motorhome.
FYI.
__________________

__________________
2018 (2017 Sprinter Cab Chassis) Navion24V + 2016 Wrangler JKU (sold @ ????)
2016 Sunstar 26HE, V10, 3V, 6 Speed (sold @ 4600 miles)
2002 Roadtrek C190P (sold @ 315,000kms)
Winterbagoal is offline   Reply With Quote
Reply

Tags
battery



Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
House battery/chassis battery/charging and start assist question Rookie RVer Class C Motorhome Discussions 5 06-06-2020 07:02 PM
Battery & Battery Disconnect Question(s) and advice needed LCDRAKAllen Newmar Owner's Forum 16 12-15-2015 08:31 AM
Another battery question - chassis battery and inverter cvbdsl Class A Motorhome Discussions 12 04-06-2015 04:30 PM
Battery Question answered, now I have a solar panel question! Lkraus3 Vintage RV's 8 02-21-2011 11:06 AM
"Fresh" water question, & Inverter/Battery question Dagwood_73 Boondocking 7 07-29-2005 01:15 PM

» Featured Campgrounds

Reviews provided by


All times are GMT -6. The time now is 04:44 AM.


Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2020, vBulletin Solutions, Inc.
×