Lithium Battery Conversion - Recap and Report

[FunSteak]

Now that battery pricing has started to come down, I took the plunge and upgraded to Lithium house batteries. I thought I'd write up what I purchased and what I did to help others considering the switch.

Our rig is a 2017 Minnie Winnie 26A, a class C. It was pretty standard, with a WFCO coverter/charger, Trombetta boost solenoid, and two group 24 lead acid batteries (<>80AH each). Batteries are located under the entrance step, and space is at a premium - no way to shoehorn larger batteries in there. Previously, I had added a Victron battery monitor and a Trick-L-Start. Other than those items, the charge system was stock.

What pretty much enabled the swap was finding good quality, group 24 100AH LiFePo batteries with built in BMS, and not for $1000 each. That hurdle was cleared earlier this year when Li Time released 100AH group 24 batteries that perfectly fit my needs. Best part? I got two for $575, shipped to my door! I believe the price has dropped a bit more since I purchased them.

These things are really, really nice. Very well reviewed. Built in BMS with all the usual safety items, hi temp, low temp, low charge, overcharge, and high discharge current are all covered. Reviewer testing shows excellent performance and confirms all the protections work as advertised. They are exactly the same size as the LA batts were, and fit perfectly.

My existing WFCO 8955 didn't support lithium charging profiles, so I replaced the charger/coverter section with something like this. That outputs 14.6V charge current (with the jumper in the correct position per instructions) and the new batts charge easily to 100%. I get about 550W of charge power from it. Very simple swap; just a few wires and two screws.

I removed the Trombetta solenoid to avoid overtaxing my alternator. This was necessary, but does have a drawback - now the "boost" switch on my dash is nonfunctional, so I can't jumpstart myself with the house batteries. I've started carrying a small jump box, just in case. The good news is that the wire that activates the solenoid is hot with 12V when the engine is running, so that was very handy for the next item I added...

To continue to be able to charge from the alternator when the engine is running, I also installed a Renogy 40A DC-DC charger. This requires a "D+" wire, which must be hot while the engine is running to enable the charger. I was able to easily repurpose the wire from the solenoid for this. Now, when engine is off, the charger is totally off and draws no power, so no parasitic drain on house batts while boondocking. When engine is on, I get around 500W of charge power to house batts. It's pretty slick.

I had to remove the Trick-L-Start, as it's not designed for Lithium and dumped a bunch of power to the chassis battery while boondocking, which is no bueno.

I made my own custom battery cables using this crimper and copper lugs. I used 0 AWG for the battery cables and 4 AWG for the DC-DC charger cables. I ran the battery cables to heavy terminal blocks to keep things clean.

Results: This upgrade is fantastic! I now have more overall Amp Hours and I can use way more of them since you can draw down a lithim battery much more than a LA without damage. It saves probably over 40 lbs of weight. It charges much faster (no current ramp down as you approach 100% as with LA batts.) As an example, when boondocking for four days previously, I'd have to run the genny for a couple hours each day to reach or get close to 100%. Now I might run it for an hour or two on day 3, if that's even necessary. When I start the engine to leave, it's at 100% well before we get home!

I'm very, very pleased. If you're on the fence about this change and boondock at all, I can't recommend it enough.

I'm happy to answer questions or fill in any details in this thread. Thanks for coming to my TED Talk.

 

[IBTripping]

Nice. Thanks for posting.

 

[ButchW]

Fantastic!…. Any pics of the installation?
Butch

 

[FunSteak]

I have a couple of photos, but stupidly didn't take one of the final, completed install. I'll get one and post it.

Here's the old setup. You can see the solenoid (now removed) and Amp-L-Start (now removed). The yellow wire on the top of the solenoid is energized when the engine is running (or when the "boost" switch is activated). That came in very handy, as I could just connect that to the "D+" terminal on the DC-DC charger so it activates only when engine on.



Here's how it looked before I realized the Amp-L-Start wouldn't play nicely and had to remove it. I wound up installing a couple of circuit breakers for the DC-DC, instead, so I could fully protect and isolate it. I'll post a shot of the final configuration soon.

 

[FunSteak]

Also, a quick field report. We just spent five nights at our favorite state park, fully off-grid. No hookups. I'm thrilled to say we didn't run the genny one time, just relying on the batteries. Packing up on the morning of departure, the Victron told me we still had 39% left! Previously, I'd have had to run it at least twice, maybe three times, for 2-3 hours each, to avoid dipping too close to 50% SOC on the old batteries. Heck, I think they wouldn't even have made it that far without going under 12V.

I'm beyond pleased with this upgrade. Worth every penny and every moment of work.

 

[Mark_K5LXP]

avoid dipping too close to 50% SOC on the old batteries. Heck, I think they wouldn't even have made it that far without going under 12V.

Why is that a problem?

Mark B.
Albuquerque,NM

 

[FunSteak]

Why is that a problem?

Mark B.
Albuquerque,NM

Going below 50% on lead acid batteries can cause damage and reduce their lifespan. Plus, when voltage gets too low, my Victron monitor alarms, my lights get flickery and water pump gets slow.

I got seven years from my old batteries by being careful and diligent with them. Even so, they just sort of lost their capacity pretty dramatically. That's how I knew it was time for a change.

The lithiums I have now are supposedly good for 10,000 charge cycles, so I'm expecting a looong life from them. Also, you can draw them WAY down, to 20% or less, without damage or even much voltage drop, so you get much more usable power from the same overall capacity.

 

[Sunnyfalls]

I hoped you eliminated having those positive and negative battery cables from crossing over each other as shown in photos. That's a recipe for disaster because RV vibration when traveling can cause the insulation to wear and fail resulting in a high amperage DC short that isn't protected by circuit breakers or fuses. You will be solely dependent on the BMS to avoid having an RV fire.

We just use a single Group 27 100AH LiFePO4, 3000W Inverter and 200 Watt solar panels to meet all our 12VDC and 120VAC power needs to do endless dry camping without ever running our small propane generator. We only need to use our generator to run our air conditioning, which we rarely need. So the only things that limit our dry camping duration is sourcing food, water and propane.

 

[FunSteak]

I hoped you eliminated having those positive and negative battery cables from crossing over each other as shown in photos. That's a recipe for disaster because RV vibration when traveling can cause the insulation to wear and fail resulting in a high amperage DC short that isn't protected by circuit breakers or fuses. You will be solely dependent on the BMS to avoid having an RV fire.

Hmm, good point on the cables. If I can't separate them well, I'll loom them and tie them together. Thanks for the tip.

 

[John From Detroit]

Why is that a problem?

Mark B.
Albuquerque,NM

On the old Lead Acid batteries they age faster at lower states of charge and below 12 volts some things. LIke the Fridge. May pop failure codes.. or just flat not work (Furnace)

 

[Mark_K5LXP]

Going below 50% on lead acid batteries can cause damage and reduce their lifespan.

To be perfectly accurate it's not "damage", it's "wear". No different than a tire that's driven on wears out quicker than one that isn't driven. And just like a tire, batteries go bad whether they're used or not so the degree of usage becomes a balance between calendar life and the service you want to get from it. All other things being equal there's very little energy delivery difference between a battery that's only discharged 20% many times, or 80+% fewer times. Because RV service has uncontrolled discharge conditions (depth, currents, frequency) it is impossible to target a specific depth of discharge to optimize any particular service life characteristic you're after. Given that most RV's aren't used more than a couple dozen times a year, the 50% Rule is a unicorn, there's no point in even trying.

The lithiums I have now are supposedly good for 10,000 charge cycles,

Lithiums have a similar cycle life/DoD curve as lead acid - the deeper the discharge, the fewer cycles you get. It could very well be the ones you have offer a 10,000 cycle life, but likely at a very shallow depth of discharge (5%?). At deep depths (90-100%) the cycle life could be as low as 1500. Not inconceivable in say an off grid application where some amount of energy is used, then replenished daily. But there's a problem with that:

10,000 cycles / 365 days = 27.39 years.

Even optimistically a lithium battery will only last 15 calendar years, so operating it to achieve 10,000 cycles you won't be utilizing nearly half of this battery's capacity, because it will age out before it wears out. Going to a battery half this size or using more of it's capacity will net you better cost efficient service life. In an application like RV's where you're only using it 20 or 30 times a year, cycle life of any chemistry is completely irrelevant. That's not to say you can't enjoy the other benefits lithium has to offer, but it is saying the argument for operating to long cycle life profiles is moot. It's moot even for lead acid. Typical service life for LA is about 7 years, and 600-700 100% DoD cycles. 7 years times 30 cycles a year is 210 cycles. Even running a LA battery 'dead' every single outing the battery will still age out before it wears out. So the idea of "preserving" any battery by limiting DoD to some arbitrary point only assures you'll be running your generator a lot more often, not using your stuff, and taking more capacity to the recycler.

On the old Lead Acid batteries they age faster at lower states of charge and below 12 volts some things. LIke the Fridge. May pop failure codes.. or just flat not work (Furnace)

Batteries *stored* at low states of charge degrade faster. Operating is a different story. If you have devices that can't function over the specified operating voltage range of the battery that's not a battery problem, it's a device or system problem. At least with the winnebago I have, every single thing in it operates properly from 12.7 down to 10.5V as it should.

For the record, I understand lithiums perform better than lead acid in almost every respect. As it stands today, it's stricly a cost/benefit balance. It's implied by the OP's post that lithium offered the capability to operate below 50% DoD due to concerns of damaging LA. That's a false assumption but I know one of the common ones used to rationalize the switch to lithium. There is still value advantages to LA in some applications. Decide what you want to do, and what that's worth.

Mark B.
Albuquerque, NM

 

[Sunnyfalls]

To be perfectly accurate it's not "damage", it's "wear". No different than a tire that's driven on wears out quicker than one that isn't driven. And just like a tire, batteries go bad whether they're used or not so the degree of usage becomes a balance between calendar life and the service you want to get from it. All other things being equal there's very little energy delivery difference between a battery that's only discharged 20% many times, or 80+% fewer times. Because RV service has uncontrolled discharge conditions (depth, currents, frequency) it is impossible to target a specific depth of discharge to optimize any particular service life characteristic you're after. Given that most RV's aren't used more than a couple dozen times a year, the 50% Rule is a unicorn, there's no point in even trying.


Lithiums have a similar cycle life/DoD curve as lead acid - the deeper the discharge, the fewer cycles you get. It could very well be the ones you have offer a 10,000 cycle life, but likely at a very shallow depth of discharge (5%?). At deep depths (90-100%) the cycle life could be as low as 1500. Not inconceivable in say an off grid application where some amount of energy is used, then replenished daily. But there's a problem with that:

10,000 cycles / 365 days = 27.39 years.

Even optimistically a lithium battery will only last 15 calendar years, so operating it to achieve 10,000 cycles you won't be utilizing nearly half of this battery's capacity, because it will age out before it wears out. Going to a battery half this size or using more of it's capacity will net you better cost efficient service life. In an application like RV's where you're only using it 20 or 30 times a year, cycle life of any chemistry is completely irrelevant. That's not to say you can't enjoy the other benefits lithium has to offer, but it is saying the argument for operating to long cycle life profiles is moot. It's moot even for lead acid. Typical service life for LA is about 7 years, and 600-700 100% DoD cycles. 7 years times 30 cycles a year is 210 cycles. Even running a LA battery 'dead' every single outing the battery will still age out before it wears out. So the idea of "preserving" any battery by limiting DoD to some arbitrary point only assures you'll be running your generator a lot more often, not using your stuff, and taking more capacity to the recycler.


Batteries *stored* at low states of charge degrade faster. Operating is a different story. If you have devices that can't function over the specified operating voltage range of the battery that's not a battery problem, it's a device or system problem. At least with the winnebago I have, every single thing in it operates properly from 12.7 down to 10.5V as it should.

For the record, I understand lithiums perform better than lead acid in almost every respect. As it stands today, it's stricly a cost/benefit balance. It's implied by the OP's post that lithium offered the capability to operate below 50% DoD due to concerns of damaging LA. That's a false assumption but I know one of the common ones used to rationalize the switch to lithium. There is still value advantages to LA in some applications. Decide what you want to do, and what that's worth.

Mark B.
Albuquerque, NM

This is well stated and is my understanding on this subject as well. The primary benefit of using lithium is their much faster charge times which then enables using smaller solar panels to quickly replenish the daily RV battery AH depletion capacity with the available daily sunlight. Other benefits of lithium are the much greater AH capacity per pound of battery and the better ROI given their longer shelf life and larger AH capacity compared to other battery chemistries.

The number of charging cycles is already far beyond what is needed for RVs. Manufacturers should now focus on increasing the maximum discharge current rating from the typical C1.0 to C3.0 so we no longer need to modify lithium batteries to get 300A from a 100AH lithium battery, which would then likely meet all the needs of most RVers who don't use batteries for powering air conditioning, refrigerators or other high and long term power applications.

 

[John From Detroit]

I just put in a Lithium to back up power to the Fridge. this is a full UPS system 2.4 KWH (The fridge uses about 1.5 KWH per day by measurement) so I should have around 40 hours of protection plus 18 hours of "Safe storage" I'm hoping power fails do not go past that.

I have room for an additional storage. And the system is designed to accept it. (Plug and socket)

My primary back up system was 300 AH of Lead acid. (About one KWH) it's about to become 300 (or more) of LI. (that' 3times the usable storage) Right now those Lead Acid batteries all tested.. Crap.

 

[FunSteak]

As promised, here are some photos of the completed install.

This is the entire under-step area.



This is the battery bay. Victron shunt is on the left. I heeded Sunnyfalls’ advice and loomed the conductors that touched or were near touching anything.



And here is the wiring area. You can see the circuit breakers - 60A from the alternator and 50A to house batts, per Renogy specs. I replaced the solenoid with a terminal post. Labeled the charging conductors to keep things easy to troubleshoot.

 

[solarman]

Why is that a problem?

Mark B.
Albuquerque,NM

LOL.. I'm with you on that one Mark, sadly this internet parroted 50% nonsense is never going away..

 

[Heli_av8tor]

Also agree, with a but…
Below 50% the batteries internal resistance has risen to the point that drawing significant current drops the voltage below the inverter drop-out voltage.

 

[Mark_K5LXP]

It can, but that's not a battery problem, it's an equipment/application problem. Internal impedance, or more directly terminal voltage under load is predictable. If it's decided up front that a specific load will be required for a given duration from LA storage batteries, the Ah and type to achieve this can be determined up front. I get that lithium doesn't have this issue near to the degree LA has, but to cite voltage drop says they're being operated outside of their application limit. If one wants to accommodate that by limiting DoD that can work, but it indicates a misapplication. You're asking a 1/2 ton truck to move 4 tons, and blaming the truck.

Mark B.
Albuquerque, NM

 

[FunSteak]

I appreciate the technical education; it's spurred me to read up further on it. Thanks.

One thing I do know with certainty is that this was a pretty significant quality of life improvement for us. More available power, much faster recharging and significant weight reduction. I'm very satisfied and happy with the cost/benefit.

 

[Sunnyfalls]

Yes, adopting a life long quest to get educated on all manner of things is preferred to arrogant ignorance bliss... People don't know what they don't know and tend to just believe what they believe.