Lithium Iron Phosphate Battery (LiFePO4) for Direct Lead-Acid Replacement

[garageman402]

I'm looking to replace the deep cycle lead acid house batteries in my RV with a Lithium battery. I currently am using (2) group 24 flooded batteries which I'd like to replace with a single 200 or 230ah LiFePO4 battery. Space limitations may force me to use (2) 100ah units closer to the grp 24 size. Invariably when its in for service they leave the battery switch turned on so they get discharged pretty close to 100%. I'm lucky to get 2 years service from these.

The question is can I just drop it (them) in? This will be charged by the vehicle alternator when driving, generator when boondocked, or shore power when available. So basically there are two charging systems in place. I've read where I'd have to replace the on board charger but how would I handle the alternator charging?

Thanks for any advice

 

[daniel327]

Get a DC-DC charger that features an LiFePO4 charge profile and install it close to the battery location.

 

[ripcord]

No, you can't just drop them in if you are charging with the alternator. LiFePO4 batteries have very low internal resistance and will draw much more current than lead acid batteries, to the point where your alternator and wiring can't safely keep up. A DC-DC charger made for LiFePO4 is needed for alternator charging. You may need to change or update the 12V power supply, too

What kind of RV do you have and what are the details of your current setup?

 

[fsdork]

For the converter (shore power to 12V DC battery charging and 12V supply for devices and appliances), there are a range of possibilities that may apply - some can be configured for lithium batteries by flipping a switch, some auto-detect battery type, and others only have a lead acid profile, so they require a board replacement or replacement of the entire converter component.

For alternator charging - as was already suggested, you'll need a DC to DC charger with an appropriate charge profile. Victron is my personal preference, but there are other good brands out there. Across different charger models, there is a wide range of maximum amperage available. Which one you go with will be dictated by how quickly you need to charge your batteries while on the road, what maximum current the wiring can handle, and how much of a load you want to put on your alternator. Without the DC-DC charger, depleted lithium batteries will try to pull a ton of current - hopefully a fuse would go first, but I wouldn't bet my alternator or burning down my RV on it.

Both components need to be considered. You could use your current lead-acid profile converter, but you won't get the batteries above about 85% from shore power alone. Not the end of the world in the short term, or if you travel enough to let the alternator top them up semi-regularly.

 

[fsdork]

Further to the current converter - I should be a bit more clear about whether using one with a lead-acid profile is OK; it really isn't. They commonly have a desulfating or repair mode which will hit your batteries with elevated voltage. This is sometimes needed to maintain lead acid batteries, but only has downsides for lithium.

 

[ctechbob]

There's a whole sister forum to BITOG devoted to RV'ing.

https://rvthe.us/community/

What everyone said here is mostly correct.

You have the advantage that you're not trying to charge through a 7 pin trailer harness, so you'll have a little more amperage available to you to do the charging.

You will need the DC/DC charger, but you'll have to take a good look at the way the camper is set up as to where you put it in the system. You've probably got some form of isolation device in there that you'll need to deal with and you'll need a place to put the charger.

Looks like your camper was built in 2020/2021 ish so your on board converter might be capable of charging LifePO4, but some of those older ones had some issues here and there with it. I don't rely on my converter anymore since I'm fully kitted out with Victron, but in all honesty I've never seen a converter that does desulfating. Most of them just float the voltage at 13.6ish when they're not doing a bulk charge, which will be fine on a LifePO4.

The other thing you need to worry about is freezing. You can't charge a LifePO4 below 32f. You'll kill them in short order. As long as you can turn off any charging to the batteries below that temp you'll be fine, or make sure and buy batteries that will disconnect themselves below that temp (or heated batts). Most do, some work better than others.

 

[jetman]

I'm looking to replace the deep cycle lead acid house batteries in my RV with a Lithium battery.

The question is can I just drop it (them) in? This will be charged by the vehicle alternator when driving, generator when boondocked, or shore power when available. So basically there are two charging systems in place. I've read where I'd have to replace the on board charger but how would I handle the alternator charging?

Thanks for any advice

1995 Prevost XL 40′ bus converted to a MH in 1996 by LibertyCoach

It’s been 4 yrs and 18,000 miles since I switched from 3 Lifeline AGMs batteries to 3 Renogy Lithium/Lifepo4 house batteries. I have had zero issues with them or my simple easy inexpensive drop-in install.

I recently did a capacity test on them, and they still have 100% capacity.

How do I keep them charged?

1) with dual Magnum MS2812 inverter/chargers that I installed almost 9 yrs ago. I programmed the remotes using the CC/CV & CUSTOM feature for the Lifepo4 chemistry and easily make adjustments to my custom charging profiles to suit our needs.

or

2) with the Prevost supplied GM air cooled 12v/145amp house alternator with its built-in voltage regulator that’s belt driven by the 90* gearbox.

The only modifications I did were:

1) Replaced the small Liberty installed battery isolator, connects the gen bat with these Lifepo4 house bats, with a normally open continuous duty 12v/300amp solenoid/relay. ($20), I ran a wire to trigger it to close when the ignition switch is in the ON position. The Lifepo4 house batts ARE connected to the lead acid gen battery, and the 12v alternator anytime the Detroit engine is running. Works perfectly.

For cold wx operations:

2) Added a 12v heat pad to each of the 3 house batteries ($30), a 3 gang switch panel ($20), and a thermostat ($20).

When we are not using the bus, we store it unplugged with the house Lifepo4 batteries at 50% state of charge (13.1v) as recommended for maximum battery life. I do not have a state of charge gauge. I go by their resting voltage. My Lifepo4 batteries have Bluetooth which we choose NOT to utilize because there is no need.

Your results may vary.

 

[jetman]

There's a whole sister forum to BITOG devoted to RV'ing.

https://rvthe.us/community/

I never knew about them.
I think I'll join.

 

[SubieRubyRoo]

For the converter (shore power to 12V DC battery charging and 12V supply for devices and appliances), there are a range of possibilities that may apply - some can be configured for lithium batteries by flipping a switch, some auto-detect battery type, and others only have a lead acid profile, so they require a board replacement or replacement of the entire converter component.

For alternator charging - as was already suggested, you'll need a DC to DC charger with an appropriate charge profile. Victron is my personal preference, but there are other good brands out there. Across different charger models, there is a wide range of maximum amperage available. Which one you go with will be dictated by how quickly you need to charge your batteries while on the road, what maximum current the wiring can handle, and how much of a load you want to put on your alternator. Without the DC-DC charger, depleted lithium batteries will try to pull a ton of current - hopefully a fuse would go first, but I wouldn't bet my alternator or burning down my RV on it.

Both components need to be considered. You could use your current lead-acid profile converter, but you won't get the batteries above about 85% from shore power alone. Not the end of the world in the short term, or if you travel enough to let the alternator top them up semi-regularly.

Probably the safest bet is, whatever LiFePo battery(ies) you decide on, buying that manufacturer’s charger is the safest bet by far. The voltages and charge profiles are completely different (but I’m not the guy to ask specifics) and who knows how robustly each of those (mainly) Chinese batteries are connected internally.

You don’t want to drop potentially $800-1k on a battery, connect it to a different brand charger and fry it, then have the warranty denied because the internal sensor shows it was fed the wrong voltage or current. Yeah, Maybe a PITB, but you don’t want a dead battery nor a lithium fire in your RV. Think about the big picture- the battery & charger is small fries compared to burning your RV & belongings down…. Even if your family isn’t in it at the time.

 

[fsdork]

Probably the safest bet is, whatever LiFePo battery(ies) you decide on, buying that manufacturer’s charger is the safest bet by far. The voltages and charge profiles are completely different (but I’m not the guy to ask specifics) and who knows how robustly each of those (mainly) Chinese batteries are connected internally.

You don’t want to drop potentially $800-1k on a battery, connect it to a different brand charger and fry it, then have the warranty denied because the internal sensor shows it was fed the wrong voltage or current. Yeah, Maybe a PITB, but you don’t want a dead battery nor a lithium fire in your RV. Think about the big picture- the battery & charger is small fries compared to burning your RV & belongings down…. Even if your family isn’t in it at the time.

If the goal is to avoid finger-pointing in the event of a failure, that makes sense. Following that thread, it would probably be ideal to use an installer who is certified by the equipment manufacturer.

Personally, I'm comfortable configuring the electronics side so it follows the profile prescribed by the battery manufacturer. Not everyone wants to get into the technical weeds, which is fair.

 

[wwillson]

What everyone said here is mostly correct.

Listen to @ctechbob he knows what he's talking about.

 

[garageman402]

No, you can't just drop them in if you are charging with the alternator. LiFePO4 batteries have very low internal resistance and will draw much more current than lead acid batteries, to the point where your alternator and wiring can't safely keep up. A DC-DC charger made for LiFePO4 is needed for alternator charging. You may need to change or update the 12V power supply, too

What kind of RV do you have and what are the details of your current setup?

Most, if not all of the batteries I've seen have a 50 amp charging current limiter, so the alternator won't have the guts sucked out of it.

There's a whole sister forum to BITOG devoted to RV'ing.

https://rvthe.us/community/

What everyone said here is mostly correct.

You have the advantage that you're not trying to charge through a 7 pin trailer harness, so you'll have a little more amperage available to you to do the charging.

You will need the DC/DC charger, but you'll have to take a good look at the way the camper is set up as to where you put it in the system. You've probably got some form of isolation device in there that you'll need to deal with and you'll need a place to put the charger.

Looks like your camper was built in 2020/2021 ish so your on board converter might be capable of charging LifePO4, but some of those older ones had some issues here and there with it. I don't rely on my converter anymore since I'm fully kitted out with Victron, but in all honesty I've never seen a converter that does desulfating. Most of them just float the voltage at 13.6ish when they're not doing a bulk charge, which will be fine on a LifePO4.

The other thing you need to worry about is freezing. You can't charge a LifePO4 below 32f. You'll kill them in short order. As long as you can turn off any charging to the batteries below that temp you'll be fine, or make sure and buy batteries that will disconnect themselves below that temp. Most do, some work better than others.

Most if not all the batteries I've seen stop charging below 32ºF & stop producing at a lower temp (they have sensors that disconnect the battery). I believe that's a BCM (Battery Charge Monitor)? Edit: it's BMS (Battery Monitoring System)

From the website: Low-Temperature Protection: Our deep cycle battery is built to perform in harsh environments from -4°F to 140°F. It automatically stops discharging below 5°F and charging below 14°F, ensuring secure and stable performance—even in extreme weather

Yes it's a 2021 house on a 2020 chassis, but it's the lower end, gas engine, no slide outs. I doubt it would have an upgraded converter. Keeping 13.6 volts when charging through the converter & 14v+ when driving seems like it would work out ok? LiFePO batteries last longer between 20% & 80% anyway.

The only desulfating chargers I've seen are the NOCO battery maintainers, maybe the Battery Tender does too.......

 

[garageman402]

2) Added a 12v heat pad to each of the 3 house batteries ($30), a 3 gang switch panel ($20), and a thermostat ($20).

Some of the batteries now have that option built in.

 

[The_Jeff]

The LifePO4+ in my off grid cabin have the battery management system but it's crude, just an on/off circuit breaker type deal. Others explained it already, but it cuts out with a charge over a very high threshold, I want to say 100 amps. Also trying to charge below freezing or discharge below, I want to say, -4F. If added without other gizmos I can see it repeatedly kicking on and off which is not good at all.

 

[ripcord]

The safety features in a LiFePO4 battery BMS are just that, safety features. You're not supposed to rely on them to limit current. It should be considered more like a fuse or breaker switch.

 

[ctechbob]

As for batteries having onboard BMS.

You're correct, most of them do have limits on charge/discharge and temperature.

But.

I've seen enough of them with failed sensors that I take their onboard BMS as a backup rather than a primary.

I have 4 batteries in parallel and my Multiplus II's max output is 120a for charging, so that is well below their limits. Even with a maxed out charging and maxed out solar I'm still at only 52a per battery charging.

I also monitor temp on the battery pack itself instead of relying on the internal sensors. The terminal will get colder faster than the internals, so that is set to 34 degrees to give some safety margin.

You also don't want to pull max current from your alternator all the time. Its not great for their lifespans. That's also a good reason for a DC/DC, you can set limits.

 

[meep]

Excellent posts here.

I just bought 2 LiFE 12V 100AH cells for about 150 each, and they are small. Made by watt cycle, recommended to me by a friend doing an ambulance build. Reviews on the watt cycle batteries show higher quality assembly for the price range. The neat thing is they are a full 100ah but smaller casing, maybe 8x9x5.5” and 25 pounds each. Mine are used in a DIY inverter box.

Main thing that was mentioned is they need a different charging profile to be happy. I’ve got an 8AH 24v victron charger that frankly is the bees knees. For DC to DC charging, you’d need a DC-DC converter to support it.

There are versions of these batteries that can self-divert some power to provide internal heat for cold weather operation.

The minimal voltage sag under load is a completely different world from lead acid. These things have some output to them.

 

[oil pan 4]

Been there done that went back to AGM.

I would use LiFePO4 in a summer only machine where the weight saving is meaningful.

 

[ctechbob]

Been there done that went back to AGM.

I would use LiFePO4 in a summer only machine where the weight saving is meaningful.

We're talking RV's here. In that world LifePO4 wipes the floor in just about every way compared to AGM.

For a Starting battery, yea, not a good choice.

 

[ctechbob]

FWIW, I've been watching a few teardowns of some Battleborn batteries lately and I gotta say. What on earth were they thinking? I expected a little better engineering out of them, but they are terribly constructed. And they're claiming that construction is a 'feature'.

They are essentially putting a thick piece of plastic sandwiched between the output terminals and saying if that junction gets hot, it is designed to fail. What happens is they don't outright fail, they get loose, cause a higher impedance connection, make more heat, melt more.

I would not recommend someone spend any money with them until they fix that problem.

There are plenty of offshore options that are 1/3-1/4 the price that perform fantastically. And are likely safer.