LiFePO4 as 2nd battery

[Komrade]

Dear Forum,

May not be the perfect forum, but the forum has surprised me on many levels so far with maturity and knowledge..

While mulling possibility of spending nearly 1K on a LiFePO4 battery and reading reviews I stumbled upon a review that talked about using this technology as an additional battery in RV.

From previous reading that seemed to be a no-no, but I also think it can be made work if it's maintained separately from existing Lead battery, and provides 80% of 'daily' needs. I am just not sure it would be worth it.

I thought I read it in one of the Battle Born reviews, but I cannot find it.

Wanted to see what more experienced forum members think on the subject.

Edit: to clarify, title should have read as 2nd "house" battery. We can ignore starting needs for purposes of this conversation

[Scalf77]

To clarify, you mean “House Battery” not a second house battery, you would not want to mix with another technology.

Looking at LiFePO4 or Lithium in general it brings with it some pluses:.

• Weight to Power Ratio
• 80% to 90% DOD without degrading life cycles.
• Not negatively affected by PSC or Partial State of Charger
• Fast Charge Rate
• Long Cycle Life compared to lead acid
• Low Peukert number

and minuses:

• High Cost of ownership
• Acceptable temperature to charge at, specifically cold, but even high temps have some impacts to life span.
• Perceived volatility, sure we have all read about Lithium Battery fires. Any time your storing power you have potentials for problems.

Many people assume that you can’t discharge your Lead Acid Battery below 50%. You can but the number of expected life cycles decreases substantially if you do. 50% just seems to be a good point for capacity vs life cycle.

PSC is the largest driving factor in killing are lead acid based battery systems. After usage they liked to be fully charged to full capacity. Solar especially in the winter months make this worse. Many people look at the voltage and assume that they got it fully charged. LiFePO4 does not suffer from this problem and one could say they almost prefer not to be fully charged.

Fast Charge rate is both a blessing and a curse. In fact, charging LiFePO4 brings its own set of issues. While some manufacturers may say they are drop in replacements, I would not consider that a true statement. Lithium batteries do not take the same stage charging that our lead acid batteries do, there is no bulk, absorption, and float stages, It is better to look for a charge device that specifically has a profile that is set up for Lithium. Even better is one that lets you program the values. The other problems with LiFePO4 is its appetite to consume power so when hooked to your alternator will lead to a early death of your alternator.

ff you want to use your Van system to charge while your driving you need a separate 2nd Alternator with a regulator that has a Lithium setting. Balmar is a common provider of these items. If only using one alternator you should go to a Battery to Battery charger that has a lithium setting. This covers two things, it can limit the charge rate and save your alternator and provide the correct charging profile. Don’t forget about Solar either, you need to make sure that your Solar charger also has a Lithium profile. There are a couple of BtoB chargers that have solar integrated in it, so that is a nice option.

When looking at installing a lithium system, the cost is high, but when you look at the lifespan it appears that the cost becomes closer to break even. The problem is that you need to realize that expected lifecycle increases to make the decision payoff. I think the reality is that we probably won’t realize the specified lifecycles that are specifying on their websites. In general, they probably have limited real life data, and a lot of data that is collected in a “Lab Environment”, there is at least one vendor I saw that states that they have seen X number of cycles in a “Lab Environment”. I appreciate the honesty.

Then there are the temperature issues, not that all batteries don’t suffer from temperature issues. Almost all the lithium vendors have some for of integrated and offer an external Battery Management System, which is a needed item with Lithium batteries. Obviously, the low temperature charging issue is the most talked about problem, especially for people going up to the slopes, or anyone that generally camps in cold temperatures. Here is where their size and weight make them an easier choice to keep inside the van, which would be hopefully help that condition.

Are they worth it? I believe if your building a system from ground up, you don’t have to change any existing equipment it might pan out, It will obviously have a higher cost to entry than lead acid system. I would cut your expectations on life cycles in ½ and see if that is a reasonable cost trade-off. I believe lithium is more of an option if you are looking for high storage capacity and some high current needs.

If I was just trying to get some of the benefits that lithium provides, I would look at Carbon Foam AGM batteries such as the Oasis Firefly. They also are not prone to PSC issues and have similar Depth of Discharges rates of 80% give you 2X the rate of AGM at 50%DOD. They also are not nearly as costly as Lithium.

Hope this helps get the discussion going.

-greg

[capnkurt]

Fantastic information, Greg. Thanks for taking the time to write that up.

I'm currently in the market for new house batteries and after looking at the Firefly batteries, I gotta say that I'm very impressed with their performance.

I like the idea of not having to worry about a thermal event (was considering going with lithium), and the limitations for charging during extreme hot or cold temps.

I have a question regarding these Firefly batteries though: can a regular lead-acid battery charger do the job (progressive dynamics PD9160A w/ charge wizard), or would these batteries need something specific for AGM?

Thanks,

Kurt

[Scalf77]

The firefly is a AGM battery, the bulk, absorption voltage is 14.4 , float is actually unneeded but listed as 13.4.


-greg

[Komrade]

Greg,

Thank you for that info. I did not have this type of battery on my consideration list.

not sure why they claim you can discharge them 80-100% w/o harming them, yet specs say that cycle life goes from 3600 @50% cycle down to 1000 @ 80%. The biggest selling point in my opinion for these seem to be that they're true "drop in". They do cost about double of a typical AGM battery, while LiFePO4 are double that.

The pros in LifePo4 are many, but I am not sure how proven it is.. Are you really going to get 5000 cycles (the claims on this vary a lot btw, which makes me question them)? The only well-warrantied battery in LifePo4 space seems to be from Relion.

Limited comparison of LiFePO4 and Firefly from somewhat local (to me) supplier
https://www.coastalclimatecontrol.co...t-brigade.html

[Scalf77]

Yes, I tend to agree they are much more drop in replacement than LiFePO4.

I am certainly not in anyway against Lithium, and like I said it would make much more sense, if you a purchasing a system that is set up for that from the get go. It would be more reasonable to purchase something that is already put together, and has some previous test time together, rather than be on the leading edge, putting all together yourself. Even testing these kind of things in a lab can be difficult.

I think as you move to high capacity battery banks it will be the way to go and more mainstream in the RV world.

-greg

[capnkurt]

Greg,

I was looking up the following B2B charger and have a couple of questions for you about the installation:

https://cdn.shopify.com/s/files/1/06...58018352701367

This seems like it would be a good product for use with flooded, AGM or even Lithium, as the output voltages are adjustable for each of the chemistries.

My first question is in regard to my system's current setup that uses a surepower isolator under the hood and a PD9100 charger/converter while on shore power. I am assuming my isolator would be removed and the B2B would be handling the isolation and charging duties while driving. However, would I also need to purchase a lithium-capable charger to replace the PD9100(with charge wizard) in order to be able to charge a lithium battery while on shore power? Or, is there a way to utilize the PD9100 to charge the starter battery while on shore power, thus making the B2B charge the house batteries as the voltage would be above 13.0?

It would be nice to be able to utilize my current charger/converter to save some costs, but is it better to not have the PD9100 charging the starter battery due to the long length of wire it would take to hook it up to the starter battery? The PD9100 is currently located under the gaucho on the driver's side of the van, near the rear wheelhouse. To me, it seems like that would lead to a pretty big length of electricity/current, since it would start at the converter/charger (while on shore power) and go all the way to the front of the van to the starter battery, and then back again to the B2B (which I would mount in an available spot next to the PD9100) before heading to the batteries, also under the gaucho.

Also, would hooking the PD9100 up to the starter battery create the possibility of a dangerous feedback if the van were inadvertently started while on shore power?

What are your thoughts?

Kurt

[Scalf77]

Originally Posted by capnkurt

Greg,

I was looking up the following B2B charger and have a couple of questions for you about the installation:

https://cdn.shopify.com/s/files/1/06...58018352701367

This seems like it would be a good product for use with flooded, AGM or even Lithium, as the output voltages are adjustable for each of the chemistries.

My first question is in regard to my system's current setup that uses a surepower isolator under the hood and a PD9100 charger/converter while on shore power. I am assuming my isolator would be removed and the B2B would be handling the isolation and charging duties while driving. However, would I also need to purchase a lithium-capable charger to replace the PD9100(with charge wizard) in order to be able to charge a lithium battery while on shore power? Or, is there a way to utilize the PD9100 to charge the starter battery while on shore power, thus making the B2B charge the house batteries as the voltage would be above 13.0?

It would be nice to be able to utilize my current charger/converter to save some costs, but is it better to not have the PD9100 charging the starter battery due to the long length of wire it would take to hook it up to the starter battery? The PD9100 is currently located under the gaucho on the driver's side of the van, near the rear wheelhouse. To me, it seems like that would lead to a pretty big length of electricity/current, since it would start at the converter/charger (while on shore power) and go all the way to the front of the van to the starter battery, and then back again to the B2B (which I would mount in an available spot next to the PD9100) before heading to the batteries, also under the gaucho.

Also, would hooking the PD9100 up to the starter battery create the possibility of a dangerous feedback if the van were inadvertently started while on shore power?

What are your thoughts?

Kurt

You are correct the B2B charger would replace surepower isolator. I am not a big fan of PD1900 with or without the charge wizard so I might be somewhat tainted in my view. It could possibly work, I would ask Sterling Power for sure before preceding, a lot depends on their front end and expectation of power input.

I am not sure that you would have to run the PD190 all the way to the battery, just connect to start battery input of B2B.

If you have every been plugged in and started your van already, you would have your answer. Seeing as your current isolator would probably already have the starting battery connected. I would have some concerns on the surge currents and spikes while starting , that the B2B normally would not see.

Kisae has a reasonably priced charger https://www.donrowe.com/category-s/1904.htm They also have two B2B chargers DMT1230 & DMT1350 both with a solar input.

-greg