Ah size of dealer-provided batteries vs what I think I need

[ChrisatUNC]

Hi all,

I can't seem to determine what the dealer-delivered battery size (in Ah) is for my 2016 FC 25 FBQ. That is, bought mine used from a dealer and it came with 2 new interstate srm-24 batteries. I did the math and that's ~160ah total. We only boondock without electrical plug-in 2 times a year (2 long weekends) and the rest of the time we're plugged in at campsites or plugged in at home where we store it because it's also my office. When boondocking we never use the inverter and use gas to reheat food instead of the microwave. We don't watch TV. Thus, the rv batteries are for lights, cellphones, fantastic fans, and gas furnace. We have a generator for recharging during the two boondock trips we make in a given year. SO - I am questioning replacing my failing interstate batteries of combined 160ah with, say, a single AGM 100ah battery.

(I know that (done right) a change from lead acid to lithium batteries will require a change to the back part of my converter box so for cost considerations (converter and lithium) I'm just proposing an AGM 100ah battery)

Am I going to encounter other issues aside from 'battery may need to be recharged more often'? Are there other reasons I should not go with a set-up below the dealer-delivered 160ah?

Sincerely,
Chris

[waninae39]

best to go with lion batteries and get as many as you can fit/afford
new 2023 AS come with NO battery. Thus you can select what you want from the dealer with losing out on a trade in like past year

also look at the victron energy products to support the lion batteries
https://www.victronenergy.com/

there are 100's of posts on this forum to help you insatll LION and related systems

[DCPAS]

I really really wanted to go with lifePO4 batteries, but ultimately decided that nobody (yet) makes one that does what I want. So I deferred by buying a couple more lead acid batteries and will re-visit this in a year or two. So, if you don't mind adding water, Walmart has a 101 amp hour deep cycle battery for $80. That will give you more amp hours than the Interstates and combined still probably costs less than one AGM.

Walmart brand: EverStart Lead Acid Marine & RV Deep Cycle Battery, Group Size 24DC

[OutdoorIdaho]

Lithium is not always the best option. Individual camping style will determine the best option.
One consideration for downsizing your battery capacity will be how much you deplete it. Lead acid and AGM batteries should not be discharged more than 50% to ensure you avoid damage. Other than that, assuming you use the same amount of ah your recharge time should not change appreciably.
So, if you will not use more than 50 ah (sounds like you won't based on the description of your use) than go for it.

[CruizinDux]

OK, time for education the lay battery owner

I currently have Deka's DP 24 in the 5th year. I'll probably swap new batts in the spring when I do the repeat our GYE's

to use DCPAS's recommendation "Walmart brand: EverStart Lead Acid Marine & RV Deep Cycle Battery, Group Size 24DC"as an example. DC is for deep cycle (translation = RV) and the EverStart 24MS is for Marine Service(?) only use??


Thx

[richard5933]

To directly answer your question, you're contemplating going from 80 usable Ah to 50 usable Ah (only half the total capacity is typically usable, as it's not recommended to run lead acid and AGM batteries below 50% of their capacity).

Having 80 usable Ah seems to me about the minimum I'd want to go, especially if you will at times be using it to run the furnace. Hit a particularly cold night and that 80 Ah might barely get you through the night. Only 50 Ah might leave you unable to stay warm through the night.

Other than the cost for the second battery, is there another reason you're thinking of only installing one?

[hairyclive]

Originally Posted by ChrisatUNC

Hi all,

I can't seem to determine what the dealer-delivered battery size (in Ah) is for my 2016 FC 25 FBQ. That is, bought mine used from a dealer and it came with 2 new interstate srm-24 batteries. I did the math and that's ~160ah total. I'm just proposing an AGM 100ah battery)

Am I going to encounter other issues aside from 'battery may need to be recharged more often'? Are there other reasons I should not go with a set-up below the dealer-delivered 160ah?

Sincerely,
Chris

You might want to wait until next season. Lithium Sulfur batteries are coming into the market and are stated to have 5x better power/weight specs, faster recharge times, and can take more charge cycles before degrading. They should also be much less expensive per KWH because they use less rare elements by weight in their construction.

https://en.wikipedia.org/wiki/Lithiu...sulfur_battery

https://www.lis.energy/

https://www.youtube.com/watch?v=mqH5yB9RB_Y

https://lyten.com/lithium-sulfur-bat...sing-ev-costs/

https://drexel.edu/news/archive/2022...te-electrolyte

https://lyten.com/lithium-sulfur-bat...sing-ev-costs/

https://www.alliedmarketresearch.com...-market-A12076

[Mollysdad]

Before rushing to lithium, if you have the stock converter, it's a single stage unit.
It does not provide a float stage that maintains the batteries. I believe they updated the converters in 2018. Look into the charging requirements of Lithium. As I recall, the single stage charger can recharge them, but it needs to stop charging when they're full.
At this time, I've decided to stick with the plain old wet cell group 24, rather than start replacing other components.

[DCPAS]

Originally Posted by CruizinDux

OK, time for education the lay battery owner

I currently have Deka's DP 24 in the 5th year. I'll probably swap new batts in the spring when I do the repeat our GYE's

to use DCPAS's recommendation "Walmart brand: EverStart Lead Acid Marine & RV Deep Cycle Battery, Group Size 24DC"as an example. DC is for deep cycle (translation = RV) and the EverStart 24MS is for Marine Service(?) only use??


Thx

The 24MS designation is for a Group 24 "marine starting" battery. So, it would be much like a car battery where it is designed to allow the high draw starter to work and be promptly recharged. It is not designed for being repeatedly deeply discharged and recharged. For lead acid batteries, 50% is a deep discharge.

[jimdelane]

Things to consider.
1. AGM vs Lithium
2. Using a lead acid charger for lithium batteries
3.Cost of a LFP charger

The cost of lithium iron phosphate (LFP LiFePO4) batteries has dropped dramatically in the past few years. When compared to AGM batteries based on usable amp hours, the cost is close. 160Ah of AGM will provide 80Ah of usable energy. That is (2) 80Ah batteries at 50lbs each. A 100ah LFP battery is 30lbs.
The AGM has 500-1000 cycles, the LFP has 3000 cycles. The AGM/SLA needs to be charged 90-100% regularly (preferably daily) to prevent sulfation which reduces capacity and not discharged below 50% which would reduce cycle life. LFP can remain partially discharged indefinitely without damage and can be safely discharged 80% while maintaining over 12.5v.

An generic 80Ah AGM/SLA batteries will cost around $150-200 ea.
A generic 100ah LFP battery will cost $350-450ea.

There has been a lot of debate and discussion as to whether a special LFP charger is required or whether a lead acid charger will work.
Basically, a lead acid charger may work. It will not fully charge the lithium battery but LFP are not damaged by remaining in a partially discharged state. He are some links to study

https://www.power-sonic.com/blog/can...l-sla-charger/

https://enerdrive.com.au/2017/11/29/...20turned%20off.

https://offroadliving.com.au/blogs/1...d-acid-charger

https://www.choosesolar.com.au/can-y...-acid-charger/

Considering what you do, you may consider going lithium. However, purchasing a LFP charger for when on shore power to top off the battery. A 10A charger can be purchased for under $100

https://www.scheels.com/p/amped-outd...hoCzwYQAvD_BwE

[ChrisatUNC]

Originally Posted by richard5933

To directly answer your question, you're contemplating going from 80 usable Ah to 50 usable Ah (only half the total capacity is typically usable, as it's not recommended to run lead acid and AGM batteries below 50% of their capacity).

Having 80 usable Ah seems to me about the minimum I'd want to go, especially if you will at times be using it to run the furnace. Hit a particularly cold night and that 80 Ah might barely get you through the night. Only 50 Ah might leave you unable to stay warm through the night.

Other than the cost for the second battery, is there another reason you're thinking of only installing one?

Thanks for your response. I was considering only 1 battery for cost and also the thought that if AGM charge a bit faster then I would only be replacing 50ah of energy (and doing so a bit faster than 50ah on a SLA battery). You make a great point about 80ah and getting through a cold night, though - thanks for that consideration.

[ChrisatUNC]

Originally Posted by Mollysdad

Before rushing to lithium, if you have the stock converter, it's a single stage unit.
It does not provide a float stage that maintains the batteries. I believe they updated the converters in 2018. Look into the charging requirements of Lithium. As I recall, the single stage charger can recharge them, but it needs to stop charging when they're full.
At this time, I've decided to stick with the plain old wet cell group 24, rather than start replacing other components.

Yes, I am aware of this factor, too. I could replace just the back of my converter/charger with the parallax 8355r, a replacement unit that has a switch o indicate lithium vs lead acid batteries. That unit was ~$300.

[ChrisatUNC]

Originally Posted by jimdelane

Things to consider.
1. AGM vs Lithium
2. Using a lead acid charger for lithium batteries
3.Cost of a LFP charger

The cost of lithium iron phosphate (LFP LiFePO4) batteries has dropped dramatically in the past few years. When compared to AGM batteries based on usable amp hours, the cost is close. 160Ah of AGM will provide 80Ah of usable energy. That is (2) 80Ah batteries at 50lbs each. A 100ah LFP battery is 30lbs.
The AGM has 500-1000 cycles, the LFP has 3000 cycles. The AGM/SLA needs to be charged 90-100% regularly (preferably daily) to prevent sulfation which reduces capacity and not discharged below 50% which would reduce cycle life. LFP can remain partially discharged indefinitely without damage and can be safely discharged 80% while maintaining over 12.5v.

An generic 80Ah AGM/SLA batteries will cost around $150-200 ea.
A generic 100ah LFP battery will cost $350-450ea.

There has been a lot of debate and discussion as to whether a special LFP charger is required or whether a lead acid charger will work.
Basically, a lead acid charger may work. It will not fully charge the lithium battery but LFP are not damaged by remaining in a partially discharged state. He are some links to study

https://www.power-sonic.com/blog/can...l-sla-charger/

https://enerdrive.com.au/2017/11/29/...20turned%20off.

https://offroadliving.com.au/blogs/1...d-acid-charger

https://www.choosesolar.com.au/can-y...-acid-charger/

Considering what you do, you may consider going lithium. However, purchasing a LFP charger for when on shore power to top off the battery. A 10A charger can be purchased for under $100

https://www.scheels.com/p/amped-outd...hoCzwYQAvD_BwE

Thanks very much for these links and look forward to reading them. In fact I do have a Noco Genius 5x2 which can handle lithium batteries. However, in an ideal world, I would want to leave all my battery connections as-is, plug in my RV to shore power at my house, AND then also connect the charger. Not sure if it would create issues for the RV to charge the batteries at the same time as the additional external charger. If I had to disconnect my batteries from the RV in order to use the external charger then I'd have to understand if there are any 12v items I'd have to go while on shore power but batteries fully disconnected. I use my airstream as an office when it's parked at the house. Any thoughts on that?

[Bill M.]

Specifically to the Walmart battery. They over rate their flooded cell batteries in their catalog description by using a non standard discharge rate. Their advertised group 28, 100 amp hour is actually a bit less than 70. I do not know how much a group 24 actually puts out.

I have never been tempted to go down in battery size for traveling. I use a CPAP so there is a considerable load on my batteries when we are off the grid.

What you risk in downsizing is drawing the batteries down more and shortening their life.

I measure my battery boxes carefully and stuff the biggest ones I can get it there. Currently have group 31 AGMs from Battery and Bulbs. 105 Amp hour. 70 lbs each. I have enough margin for tongue weight still.

To me it would be almost as easy and to just put 2 batteries back in. Disposing of the second battery and taping up the second leads take some effort. Then if you do want to go back to more power you have to buy 2 so they match and pay core charge on one of them.

[CruizinDux]

Originally Posted by DCPAS

The 24MS designation is for a Group 24 "marine starting" battery. So, it would be much like a car battery where it is designed to allow the high draw starter to work and be promptly recharged. It is not designed for being repeatedly deeply discharged and recharged. For lead acid batteries, 50% is a deep discharge.

Thanks DCPAS, cross off the MS etc and stay with the DP24 I currently have or maybe the DC24's (RV dual purpose starting/cycle service vs RV Deep Cycle service)


In fact maybe I'll call Deka again as looking at the description, possibly the DC would be better for an RV than the DP.


Thanks for the clarification

[DCPAS]

Originally Posted by Bill M.

Specifically to the Walmart battery. They over rate their flooded cell batteries in their catalog description by using a non standard discharge rate. Their advertised group 28, 100 amp hour is actually a bit less than 70. I do not know how much a group 24 actually puts out.

I just bought a couple today. Do you have support for this? I would take them back if so.

[Bill M.]

Look at the sticker on the battery that says 101 or whatever amps at a 1 amp discharge rate. Standard rating is at 5 amp. Not sure you can do any better in a flooded cell battery that size. Just understand why they seem to run down so quickly. Not pushing Battery’s and bulbs but look at their website to get a feel for sizes and ratings.

There is nothing wrong with the Walmart batteries. Just their catalog. I doubt if flooded cell Interstates have any more capacity. I used both over a number of years. You just do not have the capacity you think you do if you think the 100 amp hour number is at the most often used discharge rate .

[DCPAS]

Originally Posted by Bill M.

Look at the sticker on the battery that says 101 or whatever amps at a 1 amp discharge rate. Standard rating is at 5 amp. Not sure you can do any better in a flooded cell battery that size. Just understand why they seem to run down so quickly. Not pushing Battery’s and bulbs but look at their website to get a feel for sizes and ratings.

There is nothing wrong with the Walmart batteries. Just their catalog. I doubt if flooded cell Interstates have any more capacity. I used both over a number of years. You just do not have the capacity you think you do if you think the 100 amp hour number is at the most often used discharge rate .

Thanks. Unfortunately, it makes sense.

[CruizinDux]

Thanks Bill & DCPAS, great info.


Do either of you know the mfr?


Deka manufactures for Napa, O'Reilly's, Sam's (so possibly WM??) to name a few, all per the East Penn CS dept.


I was told if I wanted the Deka label, I could buy locally (StL) from their regional warehouse. If sticker not important the same product is via Napa etc.

[DCPAS]

Originally Posted by CruizinDux

Do either of you know the mfr?

From what I have heard, EastPenn has a solid reputation. I don't think there will be any clues on manufacturer, but I will look at the Walmart batteries this evening and see. I am ok with them being less than great (and now I appreciate that they probably merely roughly Ah equivalent with others) because I am only viewing them as a stopgap until I can move on to something lithium based.