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Jerry Work
April 25, 2022

It is Now a Near No-Brainer to Add Lithium Batteries to Your Bus

In just the last year or so prices of quality LiFePO4 batteries have dropped precipitously. At the same time, the capacity and build quality have improved dramatically. And, they are being offered in the USA by American companies with tech support by people who speak English as a first language. Much the same thing has happened to the prices, features, and quality of the electronics needed to properly monitor and recharge these batteries.

A year ago, I wrote an article for Bus Conversion Magazine about the safest, easiest, and least expensive way to add the many benefits of lithium batteries to your bus con-version, van conversion, or factory-built motorhome. You can read that article here: https://www.busconversionmagazine.com/bcm-blogs/the-advantages-of-lithium-batter-ies-for-bus-conversions/

What I suggested then, and still do, is to keep about half your existing lead-acid batteries (whether they are called AGM, SLA, flooded, or Gel Cell, they are all lead-acid batteries), disconnect them from your existing inverter/charger(s) so they only power the 12VDC loads and add a new lithium battery bank connected ONLY to the existing inverter/charger(s) to power the 120VAC loads.

I called that article “Getting the Best from Both Worlds” since you may still be able to enjoy some of the life left in your existing lead-acid batteries for the light 12VDC loads but also enjoy the many benefits of lithium batteries for powering the much more de-manding 120VAC loads.

That article was published as a four-part series in December 2020, January 2021, February 2021, and March 2021 editions of Bus Conversion Magazine.

At that time the quality lithium batteries I was using before retailed for a bit under $1,000 for 105-amp hours.

To handle recharging lithium batteries while driving I recommended the installation of a battery-to-battery charger (BtoB charger). These connect on the input side to your existing lead-acid battery bank which is charged by your alternator just as it always has been.

The output side of the BtoB charger is connected to the lithium battery bank. When the BtoB charger senses increased voltage from the alternator, it turns itself on. It converts the input power into the power needed to properly recharge the lithium batteries. (Read my previous article for more information.)

While turned on, it in effect fools the alternator into thinking the lead-acid batteries need charging (even if they are fully charged) so it keeps passing current to the lithium bank until it is fully recharged. At that point, the BtoB charger turns off, and the alternator ta-pers down as it always has until the lead-acid batteries are fully charged. All this happens automatically without the need for you to do anything.

The BtoB charger I recommended then cost a bit over $400 and was manufactured by Ster-ling Energy. If you also wanted to recharge the lithium batteries from solar panels, you also needed to buy and install an MPPT solar charge controller.

Those solar charge controllers cost just under $200 for a 40-amp unit. To know the state of charge of your lithium battery bank you also needed a quality battery monitor which costs around $200 or more. For the four 100 AH lithium batteries I used for my last article the 60-amp Sterling Battery-to-Battery charger, the Renogy MPPT solar charge controller, and a quality battery monitor the investment was just under $5,000.

Everything changed for the better during this last year!

Today a quality 300-amp hour lithium battery from a USA supplier (Rebel Batteries) owned by a disabled American Navy vet with ware-housing, shipping, warranty fulfillment, and technical support all in the USA, retails for
$1,549 including shipping. That is just over $500 per 100-amp hours of capacity. Like most lithium batteries, these are made in China and shipped in bulk to Texas where the Rebel Batteries company is located.

They not only feature a quality 150-amp battery management system with both low and high temperature shut off and all the other protections you would expect, but they also have a built-in Bluetooth battery monitor. From your Apple or Android phone, you can see and manage nearly everything associated with the battery - including the state of charge. So, you no longer need to buy a separate battery monitor.

Also new is a $300 50-amp battery-to-battery charger which also includes an MPPT solar charge controller sold by Renogy. It replaces the $400+ Sterling Energy Battery-to-Battery charger and the $200+ 40-amp MPPT solar charge controller that I recommended in the previous article.

So, your investment to add 300-amp hours of lithium now is just $1,600! To directly compare the costs, you would need to price in 300-amp hours of the lithium batteries I used for my last article, not the 400 we used. That would make the investment $3,800 then over vs$1,600 now - less than half.

Or, if you would prefer to make the comparison between 400-amp hours of the previous lithium batteries and the previous control electronics to 600-amp hours of Rebel Batteries Li batteries (two of their 300 AH units) and the new control electronics, the cost would be $3,100 - still significant less - and you wind up with 50% more total capacity.

The Rebel Batteries lithium battery and the Renogy combination Battery-to-Battery charger and MPPT solar charge controller both feature exceptional build quality. If they perform over time as well as they look coming out of the box, they will be impressive additions to your bus or van conversion.

What a change for the better in such a short time!

Keeping some of your existing lead-acid batteries to handle just the 12VDC loads and adding a new lithium battery bank to power just the 120VAC loads is still the safest, easiest, and least costly way to enjoy the many benefits of lithium batteries in your bus con-version, van conversion, or factory-built motorhome. (Again, refer to my previous article for more information on how to do this.)

The issue is that lithium batteries all have a built-in battery management system that will abruptly turn off the batteries when they reach a full charge. If you are recharging them from your alternator while driving, that can cause a large voltage spike which could be harmful to the electronics in your bus, van, or motor home.

Also, lithium batteries will accept a much higher recharge current than will lead-acid batteries. Many alternators will overheat or even burn out if they are asked to put out the much higher charge currents for extended periods.

By keeping some of your lead-acid batteries, you will not need to modify anything about the alternator charging. It will continue to work as it always has. The installation of a BtoB charger between the lead-acid and the lithium batteries will allow the lead-acid batteries to absorb any voltage spikes harmlessly and will limit the current the alternator can pass through to recharge the lithium batteries to a safe 50 to 60 amps - whatever the BtoB charger is rated for. The Sterling Energy BtoB charger limit is 60 amps while the Renogy BtoB charger is limited to 50 amps.

The BtoB charger also completely isolates the lead-acid batteries from the lithium batteries for safety. You should never directly connect these two different battery types as they operate at very different voltages - the lithium batteries output higher voltage when 80% discharged than the lead-acid batteries do when fully charged. If you connect them directly together, the lithium batteries could dangerously inrush a very high current trying to bring the lead-acid batteries up to the same voltage level.

Since the Renogy unit can also act as an MPPT solar charge controller, if you use just solar recharging, the limit is 50 amps. If you use just alternator charging, the limit is 50 amps. If you use both at the same time, 25 amps will be the limit for the solar charging and 25 amps will be the limit for alternator charging.

I use portable solar panels so the Renogy unit only sees solar when I am parked and have the portable panels plugged in. While going down the road the Renogy unit only sees the alternator charging, so I get the full 50 amps to more quickly recharge the lithium batteries.

Instead of rehashing how easy it is to create both lead-acid and a lithium part of your house battery bank, I will focus here on what is new. You can read the previous article for the details of the installation.

Let’s look at the internals of these newer, higher-capacity lithium iron phosphate batteries like the one in the photo below from Rebel Batteries. They supplied the battery shown here for this article. I asked them to send me one unsealed so I could open it up and show you the build quality. This is the same unit they used for their teardown video that you can download from their website. Even though these only cost $1,549 including shipping, the build quality is the case to a bolt and nut and lock washer on the bottom where the battery leads are attached. Those leads are fully encased in a sealant so they can never come loose and the connectors can be properly torqued without spinning. impressive.

300 Ah in a 4D size battery case fits well in many RVs.
Build quality is impressive as you can see in this photo of the BMS.

Notice how the leads going in and out of the battery management system are similarly encased in sealant. The internal battery connection leads are silicone insulated extremely high strand count wires that can easily handle the max discharge and max recharge current of 150 amps. Standard wire like what you might buy at an auto parts store cannot handle nearly that much current without over-heating. These wires can.

All internal connections are sealed - here the BMS, temp improves, balance wires.

The battery management system features very large heat sinks and is separated from the 300A LiFePO4 battery cells by an insulating layer. The cells themselves are prismatic cells that in total are only about 14” long so the outside case could be much shorter.

This is a standard 4D case that measures 20.5” x 9.37” x 8.54 inches overall including the handles so thick foam blocks are placed on each end and on the top to keep everything secure for high vibration environments like your bus, van, or motorhome.

In this picture, you can see the high and low-temperature probes, the battery balance wires, and the Bluetooth module secured with sealant as well.

The Bluetooth module is accessed by software you can download to your Apple or Android phone or tablet. The software was installed quickly and easily and connected to the battery management system the first time without trauma. It provides all the data you need to see how much capacity you have left, charge cycles, etc. Note how even the cell voltages are which is a good indication that the BMS cell balancing is working well.

Bluetooth Battery App.

This battery was manufactured in March 2021. The 300-amp hour Rebel Batteries use even larger internal wires than the ones in this one and the BMS can handle up to 16 of these batteries wired in parallel.

That is very impressive as many, even much higher priced lithium iron phosphate batteries are limited to just four wired in parallel. With this much amp-hour capacity on tap, should you ever need it in the future, you are future-proofed. The Bluetooth module automatically turned itself on when the application connected my phone to the battery to get these readings.

Important Note: There are always risks associated with being around and/or handling electricity. If you have any questions about your ability to handle these risks safely, please do not attempt to follow any of what I have outlined below and instead hire a licensed professional to do this for you. I am only sharing what I have done. Neither I nor Bus Conversion Magazine assumes any liability for what you do or how you do it.

You never knew it could be so simple, did you?

I have two 2800-watt Magnum inverter/chargers. One handles the 120VAC loads on the passenger side of my coach which includes the residential refrigerator and outdoor entertainment bays. The other handles the 120VAC loads on the driver’s side of my coach which includes the 120VAC in-duction cooktop, microwave oven, the other kitchen appliances, and the audio-video equipment.

In the original series of articles, I installed the four 100-amp hour Lion Energy batteries to power and be recharged by both of these inverter/chargers at the same time. I had them wired in parallel.

To now also take advantage of the new reBel Batteries 300-amp hour lithium battery, all I needed to do was to remove the 2/0 battery cable that connected the two inverter/chargers in parallel and connect the reBel Batteries 300-amp hour battery to the inverter/charger that was no longer connected to the Lion Energy batteries.

That meant that I nearly doubled my lithium battery capacity for powering 120VAC loads (going from 400 to 700-amp hours). This new reBel Batteries battery will be recharged while plugged into shore or generator power by the inverter/charger to which it is attached.

to which it is attached. To also have it recharge while driving (and for ease of wiring in my set up), I installed the Ren-ogy Energy 50-amp BtoB charger between the lead-acid batteries and the Lion Energy lithium batteries and the Sterling Energy 60-amp BtoB charger between the lead-acid batteries and the reBel Batteries battery. Since the Renogy unit has a built-in MPPT solar charge controller for the Lion Energy batteries, I could move my existing MPPT controller over to the reBel Batteries battery.

To handle the increase from 60-amp, charge current going through the original Sterling BtoB unit to 110 amps potentially going through both the 60-amp Sterling and the 50-amp Renogy BtoB units, I added an additional 6 AWG wire coming from the lead-acid batteries to the circuit breaker that services both BtoB chargers.

That took less than an afternoon to do and I now have the same number of lead-acid batteries serving only the 12VDC loads and nearly double the 120VAC capacity. All three house battery banks recharge automatically by the alternator while driving, the inverter/chargers while plugged into shore or generator power, or via solar when I am parked and plug in my portable solar panels. A simple Progressive Dynamics 120VAC charger takes care of the lead-acid batteries while on-shore or generator power.

Heavy internal bus bars are another indicator of quality construction.
Bluetooth module provides built-in monitoring via phone app.
300 amps fit easily inside a 4D battery case with room to spare.

Note how beefy the bus bars are and note the solid copper terminal ends, both further indications of good build quality.

This last picture shows the sturdy foam spacers holding everything in place. Note also a top foam block to prevent any up and down movement in the case once the top is sealed. Following these photos, I sealed the top on and readied this battery for installation in my Prevost XL40 Country Coach.

The new Renogy 50-amp battery-to-battery charger with a built-in MPPT solar controller exhibits equally as impressive build quality, although there is very little to see without being able to get inside the sealed case.

Renogy BtoB and MPPT solar charger in one unit.

I removed the covers on both the input and output sides in order to show the beefy connectors and the simple, four LED user interface. To install it all you need to do is connect 6AWG positive and negative wires from your lithium battery to the posts marked “Out +” and “Neg -“.

At that point, the LEDs will illuminate indicating the unit is turned on. On the left side, right above where it says “batt type” is a small button. Each time you press it, the unit will cycle through all the battery types it is designed to support. Stop when the rightmost light turns blue indicating the lithium charging profile will be output.

Then connect a 4 or 6 AWG wire coming from the lead-acid batteries to the post marked “Alt +”. If you want to also use solar panels to recharge your lithium batteries, connect the solar panel positive wire to the post marked “PV +” and the negative wire to the post marked “Neg -“ on the right side. The unit is set up and will work to automatically recharge your lithium batteries from the alternator.

Here is what it all looks like fully installed. That appears to be lots of wire until you realize that the wire supplies all three kinds of charging for all three different kinds/models of batteries. Now it seems more reasonable.

Completed installation with charging for both AGM and Lithium batteries while driving, plugged in via generator or solar, all in the original battery bay.

I normally recommend installing lithium batteries inside the coach so they won’t see extremely low temperatures that could cause a low-temperature disconnect. In this case, I don’t plan on being in cold weather in the future so I used an open 4D bay at the forward end of the battery compartment as a convenient place to install the reBel 300 Ah lithium battery.

Across the top are the two white 2800W Magnum inverter/chargers. The one on the left is powered by the new reBel battery. You can see the red and black 2/0 wires that connect the two. That inverter/charger supplies the 120VAC loads on the passenger side of the coach. The inverter/charger on the right is connected to the four 100 Ah Lion Energy lithium batteries located in a drawer in the bathroom directly above this compartment.

This inverter/charger powers the 120VAC loads on the driver’s side of the coach. The remaining three of my original 220Ah AGM lead-acid batteries that now power only the 12VDC loads are located in the lower part of the battery compartment to the left of the reBel Battery.

Solar MPPT chargers.

The next row down on the left is the three solar charge controllers. The leftmost one charges the AGM lead-acid batteries. The middle one charges the 300 Ah Rebel Batteries lithium battery. The one to the right is the new Renogy 50A BtoB and MPPT solar charger, and it is used to charge the 400 Ah of Lion Energy lithium batteries.

The red and black wires in the picture are the connectors for my portable solar panels. When not in use they just sit off to the side out of the way.

In the center of that row are the two BtoB chargers. The black Renogy unit charges the Lion Energy batteries while driving and the white Ster-ling unit charges the reBel Batteries battery while driving.

The new reBel Batteries 300 Ah lithium battery is installed in an open slot once occupied by another lead acid AGM battery. You can see it on the right in the pic below.

BtoB chargers for both Li banks.

Red 6 AWG and 4 AWG wires coming from the positive side of the AGM pass up through a hole (just in front of the Progressive Dynamics chargers) to go to the circuit breaker shown in these pics. From there one 4 AWG wire goes to the input side of the Renogy BtoB charger, and one 4 AWG wire goes to the input side of the Sterling BtoB charger.

300 AH Li-battery in 4D size on right is smaller than the 120 (available) Ah 8D AGMs to the left.

That gives plenty of amp carrying capacity to provide up to 50 Amps of alternator power passed through the Renogy BtoB charger and up to 60 Amps of alternator power that passes through the Sterling BtoB charger to keep the lithium batteries fully charged while driving.

When parked for long periods plugged into shore power, I open this circuit breaker so the higher voltage coming from the Progressive Dynamics battery charger for the lead-acid batteries won’t unnecessarily turn on both BtoB chargers. That wouldn’t hurt anything, but there is no need for them to be on in that condition.

Everything buttoned up, battery cover in place, and ready for the road.

This is the simplest, safest, and most cost-effective

way to wind up with more than 300 accessible Amp hours of lead-acid batteries to power only the 12VCD loads and 700 accessible Amp hours of lithium batteries to power all your 120VAC loads. And, everything automatically recharges from your existing alternator while driving, from shore or generator power while parked, or from solar power while you are off-grid.

Article written by Jerry Work

Jerry Work spent his professional career in technology management, first as the founder and CEO of two moderate-sized computer software companies and then as the Associate Laboratory Director for the Pacific Northwest National Laboratory (PNNL), one of the DOE multi-program laboratories. At PNNL, in addition to overall Laboratory management, he oversaw the laboratory’s work in the energy, transportation, medical and information technologies.

After retirement, he and his wife Sharon purchased a Beaver Patriot motorhome and began a cold turkey four years of full-timing which they enjoyed greatly. They then purchased a 1907 former Masonic Temple in rural Southern Oregon, restored the building and remodeled it into his studio and gallery on the first floor and living quarters on the second floor. There he designs and handcrafts fine furniture. He is well known for his many articles and tutorials about how to get the most from Festool and other-high end woodworking products.

They purchased the first of what became two fully restored GMC motorhomes, those iconic and swoopy front-wheel drive units from the 1970’s. They found the second of their two GMC’s in an air-conditioned building in Naples, FL, with just 11,000 miles on the clock following a ground-up restoration in 1984. Both of those motorhomes found their way from Mexico to Alaska and from the West to the East coast. He wrote extensively about his experiences with GMC’s and gave many a presentation at GMC club events over the years.

A few years ago they decided to go back out on the road again for longer periods of time than they could support in the GMC motorhomes so purchased a low mileage 1997 40 foot Country Coach Prevost bus conversion which is now home for more than six months out of the year. Visitors always welcome no matter where in their travels is their motto.

You can reach Jerry Work by email at:

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