Batteries, the age old question

[Nwcid]

I know all of the advantages of lithium batteries, but unless I am doing something wrong, I can not make the math come out to choose them.

In my last RV I had 4x225ah FLA batteries that got minimal maintenance and were just starting to show their age after 8 years.

My new RV has many more things that take 120v power and I have a Magnum MSH 3012 inverter that I will install when the snow goes away.

Right now I am looking at 6x225ah AGM batteries. This gives me 675ah with a 50% of 337.5ah. Cost is $1350 to my door. Down side is the weight at 430lbs.

I have the space and the funds to do 8x225ah AGM batteries which gives me 900ah with 450ah usable. Cost is $1775 to my door. More power is always nice, but this pushes the total battery weight up to 576lbs.

Looking at 2x100ah lithium batteries I would have 100ah available at 50% and 160ah at 80%. Cost is $1900. The weight is a minuscule 60lbs.

To get 3x100ah lithium I am $2700, but that just gets me right to 240ah at 80%. My understanding, is that even with lithium using it below 50% reduces the life. Even with that, the rated cycles at 80% is still higher than AGM or FLA.

While I would like lithium I can buy 2 full sets of AGM and still be money ahead. I would like to keep my spending under $2000, but I am a little flexible. The more I save, the more I will have to put toward my solar system.

Am I missing something or doing math wrong?

[C.Martin]

Originally Posted by Nwcid

I know all of the advantages of lithium batteries, but unless I am doing something wrong, I can not make the math come out to choose them.

In my last RV I had 4x225ah FLA batteries that got minimal maintenance and were just starting to show their age after 8 years.

My new RV has many more things that take 120v power and I have a Magnum MSH 3012 inverter that I will install when the snow goes away.

Right now I am looking at 6x225ah AGM batteries. This gives me 675ah with a 50% of 337.5ah. Cost is $1350 to my door. Down side is the weight at 430lbs.

I have the space and the funds to do 8x225ah AGM batteries which gives me 900ah with 450ah usable. Cost is $1775 to my door. More power is always nice, but this pushes the total battery weight up to 576lbs.

Looking at 2x100ah lithium batteries I would have 100ah available at 50% and 160ah at 80%. Cost is $1900. The weight is a minuscule 60lbs.

To get 3x100ah lithium I am $2700, but that just gets me right to 240ah at 80%. My understanding, is that even with lithium using it below 50% reduces the life. Even with that, the rated cycles at 80% is still higher than AGM or FLA.

While I would like lithium I can buy 2 full sets of AGM and still be money ahead. I would like to keep my spending under $2000, but I am a little flexible. The more I save, the more I will have to put toward my solar system.

Am I missing something or doing math wrong?

The math is different for everyone. If you hold your LiFePO4 at a comfortable temp and live OFF grid, they are the better alternative. I’m guessing that you do not spend the majority of your time off grid. AGMs will not last 10000 cycles to 50% depth of discharge. But, if you stay plugged in and only discharge 5-10%...heck, they last a very long time.

If I had to make a recommendation...I would say if your coach is plugged in 90+ % of the time...get AGMs. If your coach is plugged in less than 50% of the time...and you have a way to keep them in a moderated temp. environment...Li is a much, much better choice. In between...the decision is a bit tougher.

There are intrinsics...

Weight
Lower Peukert Constant
No sulphating if not kept at 100% a lot of the time.
Higher voltage...meaning your appliances draw fewer amps to do the same work. And voltage curve is pretty darned flat.

[astrocamper]

The advantage of the LiFePO4 batteries is the weight, more efficient charging to %100, able to sustain high current output for inverter use and higher voltages throughout the discharge cycle.

Disadvantage is cost and more temperature sensitive. It is better to keep them in the inside away from extreme heat or cold.

You don't mention if you are currently charging via shore power, alternator, generator or solar. You also don't mention how long you stay off grid and what your typical power needs are away from the grid.

[Nwcid]

My previous unit had 450ah (225ah x4) of FLA. I had ~500 watts of solar that kept it charged most of the time. I was using a 1000 watt inverter that basically just ran the tv, laptop and charging minor things. It was plugged in over the winter as the panels usually got covered by snow. We did use it a few times during the winter and with shorter days it usually increased the generator run by about 2hr/day.

We 99% of the time boondock. I am looking at putting 640 watts of solar on, but that will not happen until early summer. There will be a couple of months that the generator will be used to charge. With my previous unit the was very self sufficient when the sun was out. I am looking at a higher reserve for shorter days, cloudy days or smokey days in the PNW summers.

The batteries will be mounted under the bed so they are temperature controlled that way. However when the unit is not being used it can range from below 0*F to 120*F. I could add a switch controlled heating pad for the winter storage months.

To get 320ah of usable lithium I am looking at $4000, unless there is a deal out there I am not aware of.

I want lithium, I like lithium, I am just struggling to justify cost right now. I know over time they do pay off also. In reality I can add 6 AGM now and in 5 years ($270/year or the cost of 2 tanks of fuel in the TV) or longer, when I need to replace them I upgrade to lithium.

[BCam]

Personally, I'd still put lithium batteries in the "early adopter" stage and would wait. Like most new technology, prices will drop and new alternatives will come available.

Full Disclosure: I'm still using Costco lead acid golf cart batteries and haven't even made the leap to AGMs.

[Persistent]

Originally Posted by Nwcid

I know all of the advantages of lithium batteries, but unless I am doing something wrong, I can not make the math come out to choose them.

In my last RV I had 4x225ah FLA batteries that got minimal maintenance and were just starting to show their age after 8 years.

…

Originally Posted by Nwcid

Am I missing something or doing math wrong?

I can add a little to your math, but it is still up to you to decide because there are so many other variables.

"In my last RV I had 4x225ah FLA batteries that got minimal maintenance and were just starting to show their age after 8 years."

This probably means the equivalent of about 300 full discharge cycles, or about 600 50% discharge cycles.
Your next lead/acid batteries will probably do the same assuming you do not change your use or maintenance habits.

10000 cyc LI / 300 cyc LA = 33 life times available from lithium batteries. You will probably never need to replace the LI again in your life time.

Flooded deep draw batteries are sensitive to discharge below 10%. Planning for a limit of 50% draw down may be prudent. Many people do.

Sealed AGM deep draw batteries are not so sensitive to discharge below 10%. Most are protected by the chemistry in the AGM battery. Planning for a limit of 20% draw down is would be prudent.

Li batteries are the same as AGM in this respect. Most drop-in replacements are protected against excess draw down. It may be prudent to plan for a 20% minimum. (You don’t want to run out of power.)
So, you can use about half as much AGM or Li capacity in place of Flooded.

You will have to replace the AGM’s in half the time that you would with twice as much flooded capacity. So you are back to needing the same amount of AGM’s to get through 8 years, half for the first four years, half for the second four years. On the other hand you would be carrying around half the weight of AGM for the 8 years.

“Right now I am looking at 6x225ah AGM batteries. This gives me 675ah with a 50% of 337.5ah. Cost is $1350 to my door. Down side is the weight at 430lbs.”

The above numbers work for flooded cells but not for AGM’s.

Two AGM 225 ah at 80% = 360 amp hours good for 4 years. That would be $450.

Three Li 100 ah at 80% = 300 amp hours good for the rest of your life. That would be $3000.

No matter how you look at it, it is cheaper to get the AGM’s. Unless you increase amount of charge/discharge you do, you will not recover the value in the Li during your life time. If you used the 10000 cycle Li in ten years, you would need multiple banks of AGM's to cover that time period.

Get the AGM’s and have a lot left for the solar.

Yes, a lot of people will say draw down below 50% is a battery killer, but the published test data from one AGM battery manufacturers extensive life testing says otherwise. My experience with sealed GEL confirms. Even flat discharge does not do serious damage to Gel’s. The same is true of deep draw AGM’s. The chemistry in these types of batteries is different. It prevents significant damage to the plates in deep draw.
It is the number of full discharge cycles that matter. You can get twice as many ½ charge cycles, but that still equals the same equivalent full discharge cycles.

[followingsea]

Originally Posted by Nwcid

Am I missing something or doing math wrong?

What you are missing is an understanding of the law of of diminishing returns. What you are doing wrong is missing the point of camping.

Less is more!

My 4 golf cart batteries get the job done. The only reason I need a 2000w inverter is to run microwave.

I am retired and full time in the MH. When camping (boondocking), I use a French Press to make coffee as an example of a way to reduce electricity use.

Batteries are batteries. There is no rule that says you can not spend 2 to four times what most people do. There is no rule that says you have to turn off the huge TV and sit by a campfire either.

So if you are asking how to save money, start by figure out what is the minimum you need. This particularly important when you are storing electricity in an RV.

Here is an example of to illustrate less is more. One year I got a set of 12v path lights for Christmas. Because the lights were incandescent, the 120 v to 12 v transformer was the most expensive part. The transformer was bad so I took it back. I exchanged it for an led set with a small 10 watt transformer and got twice as many path lights.

So less current (power) results in more light.

In the case of a RV, less also means less wight.

[Smitty77]

No right or wrong on this, just choices....

I would have gone to Lithium when I replaced my previous bank of Lifeline's, but, Lifeline made me an offer for replacements I could not refuse. (Just out of warranty at 5 1/2 years, and I had a bad combination of settings between Shore Power charger and Solar Controller - that eventually walked my bank down.)

Why I had planned to go to Lithium at that time, was:
> Lower weight (And, I'm getting a heavier toad, so that diet of weight would have helped!)
> Faster recharge times
> Long enough 'expected' life to justify the up front higher expense

I think two reasons have kept Lithium Drop In's from becoming the go to battery in RV's and Boating:
1) The upfront costs of purchase is more then many are willing to pay. As well as the complexity of changing over other charging sources to support. For example, the alternator.
2) Ongoing maturity and refinement of the art of Lithium care and feeding (From just the last 5-10 years, Lithium has evolved from many building their own bundles, adding their own BMS - to now Drop In's, with all in one BMS of different levels of sophistication. Also some in the last few years, are providing BT connectivity with pretty nice APP's. (These are purposely oversimplified examples of the ongoing evolution.))

As I hope to not need another bank for 7 or so years, I'm expecting to see ongoing evolution and refinement in Lithiums, and I'd also welcome a drop in price too!

IMO, if a person is a heavy boon docker, Lithium has a higher payback in usage ease of fast charging, and not needing to be fully recharged, over Wet/AGM's. So that kind of usage makes the nod more favorable to go Lithium.

Best to all, may the power be with you, and the charge,
Smitty

[McRod]

Your not missing anything. The $/AH is still a better value for AGM and even better for FLA batteries than for any Lifepo4 battery on the market. There is no math you can do to change that.

Lot of hype for LifePo4 which Im glad, it will keep getting the price to drop. They are better batteries, but the cost is not there yet.

[PbdBlue]

Lithium is a pretty mature technology and the demand for lithium batteries is very high as they are used in almost every battery powered device, cars, etc and now batteries for home energy supply (i.e. Tesla Powerwall, LG, etc). The price drop has already occurred and most experts believe that the price will probably stay flat if not maybe even rise a bit in the future. There's a lot of research going on and who knows what the future will bring but for now it doesn't look like Lithium prices will drop much.

[radar]

The price drop for Lithium in car applications seems quite profound, especially for Tesla, but that has a lot to do with scales of operation. Eg, minor players like GMC/Chevy producing a 1000 cars per month are paying almost twice as much as Tesla who makes more than a 1000 cars per day. Even worse for ford which produces only a few hundred cars per month. This is the same effect that causes the type of lithium batteries we use in our EV’s to be outrageously expensive. I would consider them but not at current prices. Something we are following though. Both our vehicles are electric. Maybe if one them packs it in some day I’ll shoe horn one of the batteries into the pusher. .

[Nwcid]

Here is an update.

I ended up with 6 AGM.

I got the system half installed last week, will be finishing it this week.

Here is an early image of the start of the battery box with batteries in place.

[Brecklundin]

Haven't read entire thread but it's worth considering a salvaged Tesla battery from a model S.

The chemistry is different so proper precautions are required but simple to implement. In exchange you get about 5.4KWh of capacity. With 1200w or so of solar you end up with a very solid power source. Nice part is you have a system cobbled together that will give you lots of off grid freedom.

[Nwcid]

Originally Posted by Brecklundin

Haven't read entire thread but it's worth considering a salvaged Tesla battery from a model S.

The chemistry is different so proper precautions are required but simple to implement. In exchange you get about 5.4KWh of capacity. With 1200w or so of solar you end up with a very solid power source. Nice part is you have a system cobbled together that will give you lots of off grid freedom.

Well the thread is that they systems is already installed, shown in the previous post.

I did look at them but I already had a 12v inverter and working on the ups and down from 24v was more of a challenge then I had time for.