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Old 12-22-2024, 11:37 PM   #1
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Class A - Replacing Lead Acid with Lithium Ion - Amp Hours?

Good Day! My Flooded Lead Acid batteries are coming up on time for a life cycle change. I am considering changing over to Lithium Ion but when I try to research my requirements I find most of the information on this forum and other sources is overly technical and is so complicated that it fries my brain trying to read through it.

My reasons for wanting to switch are reduced maintenance and reduced weigh.

My rig has a Magnum Inverter/Converter that can be programmed for charging Lithium Ion. I currently have 4 6v FLA batteries I will be looking to replace.

My primary question at this point is how many Lithium Ion Amp Hours do I need when replacing FLA. My understanding is that 4x6v FLA provides 400 Ah but you only have access to 50% so real world you have 200 Ah at peak performance. If that math is correct and my current battery bank has always been sufficient for my needs is it reasonable to assume I can replace the battery bank with a single 12v 200 Ah Lithium Ion battery?

Thanks in advance for your thoughts!
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Old 12-23-2024, 12:58 AM   #2
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Personally I would go with 300 AH to have that little extra. You actually had 400 with the 4 sixes in a pinch.

I'll be doing basically the same thing in 2-3 years and will probably go with 400 AH just too be on the safe side. And the prices are dropping every year.
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Old 12-23-2024, 01:54 AM   #3
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FWIW:

I have 2 @ 200 aH Renogy AGM batteries, and 600 watts worth of roof panels.

Supplies me with everything I need to ignore my generator (unless I hit a rainy or snowy spell.)

When these batteries start aging out (they're at 6 years old now) I'm switching to 2 @ 100ah lithium batteries. Cheap ones.

That should keep me very close to where I am today, for less money.

(But I'll likely disconnect from alternator charging of house batts. Don't need it, don't want to buy a dc-to-dc charger.)
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Old 12-23-2024, 03:45 AM   #4
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Originally Posted by Griswald One View Post
,,, If that math is correct and my current battery bank has always been sufficient for my needs is it reasonable to assume I can replace the battery bank with a single 12v 200 Ah Lithium Ion battery? ,,,
Technically yes a single 200 Ah Lithium should replace the four 100 Ah lead acid batteries with little to no loss of energy storage capacity. Personally I consider what Unplanned Tourist suggested and increase the bank capacity with an additional 100 Ah.
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Old 12-23-2024, 03:48 AM   #5
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300 may be the way to go

I do like the idea of the 300 to give me a little extra capacity. I will have to look at measurements and see what fits in my existing trays.

I will have to do some research on the need for a DC to DC Charger. Some posts suggest you don't need it with a single Lithium battery, although I am not sure a 300Ah battery is what they have in mind. We tend to camp from power source to power source so the batteries are rarely discharged when travelling and outside of the fridge there is no significant draw on the power supply.
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Old 12-23-2024, 09:43 AM   #6
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200ah should be fine then. A lot depends on how you'll use them. If you have solar charging all day and use 390ah over night, then 200ah of Li is not going to replace the lead. If you drive an hour and get enough charge to last your typical overnight with 100ah, then 200ah of Li might charge faster than the 400ah of lead. or if you like to run the generator for the microwave and don't want to run it any more than an hour each day, Li is great for a fast charge.



There are other options besides a DC to DC on a class A, the voltage difference to drop charging amps is not that great. Li takes a big charge because of very low resistance, that low resistance also means that a small voltage drop will drop that amperage. So eliminating the 2/0 connection between the house and chassis and replacing it with a few feet of 10,12 or 14G is probably enough to protect the alternator.
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Old 12-23-2024, 10:04 AM   #7
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Originally Posted by Griswald One View Post
Good Day! My Flooded Lead Acid batteries are coming up on time for a life cycle change. I am considering changing over to Lithium Ion but when I try to research my requirements I find most of the information on this forum and other sources is overly technical and is so complicated that it fries my brain trying to read through it.

My reasons for wanting to switch are reduced maintenance and reduced weigh.

My rig has a Magnum Inverter/Converter that can be programmed for charging Lithium Ion. I currently have 4 6v FLA batteries I will be looking to replace.

My primary question at this point is how many Lithium Ion Amp Hours do I need when replacing FLA. My understanding is that 4x6v FLA provides 400 Ah but you only have access to 50% so real world you have 200 Ah at peak performance. If that math is correct and my current battery bank has always been sufficient for my needs is it reasonable to assume I can replace the battery bank with a single 12v 200 Ah Lithium Ion battery?

Thanks in advance for your thoughts!
Awful lot of mis information out there making the upgrade much more difficult and expensive than it may need to be. Here are the considerations:
1) Where are your batteries mounted? Inside or outside compartment? Do you need to use them in below freezing weather?
2) What are the largest peak loads? Are you supporting an inverter(s)? What size? How long?
3) Are you also starting a generator.
4) If maintaining engine alternator charging, what size is the alternator? Would you consider an upgrade?

The later generation of Batteries have extremely smart BMS system that can control most of what is needed and adding DC-Dc converters and stuff is fluff. Same for fancy chargers. Answer the questions above and I can put together a proper battery plan for a "drop-in" installation.
P-Mail me at d23haynes57@hotmail.com or dennis-vw-service@outlook.com.
I can set you up.
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Old 12-23-2024, 10:27 AM   #8
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My understanding is that 4x6v FLA provides 400 Ah but you only have access to 50% so real world you have 200 Ah at peak performance.
Real world LA Ah is 400Ah. Battery specifications are not imaginary. If you have been operating your LA at 50% consistently then you will be used to only using 200Ah, and a 200Ah Li battery will work for you just fine. But per above the loads might matter (peak currents) and that's the Li specification to work within with Ah being secondary.

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Old 12-23-2024, 02:45 PM   #9
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My strong suggestion: Everything you are doing is almost a complete GUESS if you don't have a battery monitor such that you actually know how many AHs you typically use per day. A really, really, really useful thing to have on any RV is a battery monitor showing you basically the exact state of charge on your battery bank, and how many AHs are flowing in/out.


With a battery monitor, you would know how many AHs you typically use per day. For example, if you already know that you never use more than 50AH per day and you are never unconnected to power between campsites for more than 1-2 days, then you are probably safe to have just a 100AH battery bank (....remember, if you aren't connected in YOUR scenario it is likely because you are DRIVING to your next campsite and your alternator is charging your battery bank while you are driving...).


With a battery monitor, you also know if your alternator is working correctly and charging your batteries. You know if your solar (if you have any) is working correctly. You know if your converter/charger is working correctly when you are plugged in. You know exactly how much battery AHs you need. You know when your batteries are getting low. You know how much current/AH each item in your RV uses. You know how much parasitic draw when you THINK everything is off. Etc...


So nobody here can answer your question accurately. Nobody here (maybe even you) knows if you use 50AH/day or if you are using 320AH/day. Until you know how many AHs per day you use, it is all just a guess.


Here is one I installed for ~$50. Works great.
https://www.amazon.com/gp/product/B07FGFFHC6



Good luck!
Chris
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Old 12-23-2024, 02:55 PM   #10
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My primary question at this point is how many Lithium Ion Amp Hours do I need when replacing FLA. My understanding is that 4x6v FLA provides 400 Ah but you only have access to 50% so real world you have 200 Ah at peak performance.

This is not correct/accurate. You currently have ~400-420AH worth of battery capacity. You can use 80% of it (or more) and you will likely never see a downside. At 80% depth of discharge you likely have ~500 full cycles.


Do you think you have boondocked and drained your batteries 500 times? Or do you think you have realistically only done that 5-20 times?


One of the main issues with drawing down your lead acid batteries to 70-80% discharged is your voltage will start to drop as the state of charge goes down. For many things, this doesn't matter (lights, fans, propane fridge, water pump). One place it DOES matter is if you are relying on the 120v output of an inverter. At some low voltage point, it will shut off and then you won't have 120v power. So if this is important to you, then yes you don't want to draw down your batteries too low. But if this isn't a major concern then you have no issue draining your lead acid battery 70-80% before recharging.


Most RVers will NEVER come close to using up all their battery's cycles so it makes absolutely no difference for most RVers if they draw down 70-80% (unless they are using an inverter).


-Chris
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Old 12-23-2024, 03:03 PM   #11
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My reasons for wanting to switch are reduced maintenance and reduced weigh.

These ARE perfectly good reasons for wanting to switch to lithium. These are 2 of the many reasons lithium batteries are better than lead acid.


But without knowing how many AHs you are actually using you won't know how much lithium AHs you need.


If you are trying to save money and reduce complications, here is another possible solution for you that achieves part of your goals/reasons... If you almost exclusively camp at full hookup sites and rarely boondock, you could probably get away with replacing your FOUR 6v GC batteries with just TWO new 6v GC lead batteries. You will cut your weight in half. You won't have to worry about your alternator or adding a DC-to-DC charger, etc. This would be an even more attractive option if you added a battery monitor now (before making this decision) and observing first that currently you are only really using 50-100AHs max on your batteries when you go camping (in between hookups). Just throwing this out there.


Good luck!
Chria
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Old 12-23-2024, 03:12 PM   #12
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Quote:
Originally Posted by Griswald One View Post
Good Day! My Flooded Lead Acid batteries are coming up on time for a life cycle change. I am considering changing over to Lithium Ion but when I try to research my requirements I find most of the information on this forum and other sources is overly technical and is so complicated that it fries my brain trying to read through it.

My reasons for wanting to switch are reduced maintenance and reduced weigh.

My rig has a Magnum Inverter/Converter that can be programmed for charging Lithium Ion. I currently have 4 6v FLA batteries I will be looking to replace.

My primary question at this point is how many Lithium Ion Amp Hours do I need when replacing FLA. My understanding is that 4x6v FLA provides 400 Ah but you only have access to 50% so real world you have 200 Ah at peak performance. If that math is correct and my current battery bank has always been sufficient for my needs is it reasonable to assume I can replace the battery bank with a single 12v 200 Ah Lithium Ion battery?

Thanks in advance for your thoughts!
I had 4 6 volt batteries and replaced them with one 400 AH lithium battery 2 years ago. Problem solved.
That said I put mine inside so it wouldn't freeze. You could go smaller but why not take real advantage and increase your capacity?
Either way I would go with only a single battery to stay with only 1 BMS.
One 200 AH will save you a whole bunch of weight.
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Old 12-23-2024, 03:44 PM   #13
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I had 4 6 volt batteries and replaced them with one 400 AH lithium battery 2 years ago. Problem solved.
That said I put mine inside so it wouldn't freeze. You could go smaller but why not take real advantage and increase your capacity?
Either way I would go with only a single battery to stay with only 1 BMS.
One 200 AH will save you a whole bunch of weight.

I 100% agree that if you were happy with four 6v GC batteries and never ran out of battery power before, adding a 400AH lithium battery will certainly make it so that you won't run out of battery in the future. 600AH, 800AH, or 1000AH would also work in this situation.



But if someone never really needed four 6v GC batteries to begin with, and they only really ever only needed two 6v GC batteries, then getting 400AH worth of lithium would be money wasted.


Without a battery monitor, or without accurate measuring with a simple voltmeter (after allowing ample time resting without a load), a user will not know how many AHs they actually need in their battery bank so that they can make the best value decisions.



-Chris
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Old 12-24-2024, 12:36 AM   #14
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Measuring daily usage not really viable

Thanks to each for their input... I understand the multiple suggestions to measure normal daily usage... but realistically there is no daily norm, it changes with the circumstances. Most days will be 0 Ah as we are plugged into shore power. Some days may be 100 Ah because I turned the fridge on at the storage yard to precool it.

REV Group, Thor and every other manufacturer optimizes (to some level) their rigs for the average user. When they sell a motorhome they know most of their users will have three power consumption modes... Storage, driving and powered camping. I am exactly the normal customer they anticipate. My rig is either in storage or in use with some kind of external power, be that alternator, generator or power post.

The only time my batteries face significant draw is when I turn the fridge on a day before departing to precool it or in the unlikely event we stop in a Walmart parking lot over night.

REV, Thor and pretty much every other modern manufacturer of Class A Gas Powered Motorhomes seems to have settled on four 6v batteries as being the preferred set up for their average user. This suggests there is some knowledge, thought, science that has gone into that decision making which would include power consumption, weight and cost. For me the set up they provided has worked well. That being said I would now like to match the provided power while reducing the overall weight, which I know means additional cost.

So if REV was building my rig today but decided to switch to Lithium... Would they match the 400 Ah available if you completely drain and potentially damage the FLA set up. Or would they drop in 200 Ah of Lithium to match the recommended maximum consumption of those FLA's... Or maybe split the difference at 300.

I suspect, if I consider the advise you have all provided up to now... I will be looking at either 300 or 400Ah in a single battery configuration. I will need self-heated for cold weather charging and I will have to look into the quality of the BMS to determine whether I need to look at a DC2DC Charger or disconnect the alternator, ideally neither.
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