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 is 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.

In December 2020, when I wrote the first article in this series on The Advantages of Lithium Batteries for Bus Conversions, I had no expectation that in the intervening two years the quality of available LiFePO4 batteries would increase so dramatically nor that the prices would fall so dramatically.  I only knew that once freed of the very high amp draw demands of powering inverters to provide 120vac power, the existing lead acid batteries (AGM, flooded, sealed) would last a long-time powering only the 12vdc pumps, fans, and LED lights in the coach.

As a result, I saw no reason to replace all of the existing lead-acid batteries at the same time, as you can read in my previous article Best of Both Worlds – Combining Lead-acid and Lithium Batteries in your Bus Conversion RV. And, there was one very good reason to leave at least one lead acid battery in the system - as a means of absorbing any voltage spikes that might occur if the battery management system controlling a LiFePO4 battery suddenly shut off when the battery became fully charged while the engine alternator was still spinning.  

Keeping at least one lead acid battery in the system also meant that the existing engine alternator could be used without modification to charge one or more LeFePO4 battery banks through Battery-to-Battery chargers.  

Those considerations lead directly to the topology I have shown in the previous articles in this series and graphically depicted in the diagram above.  Let’s review what we previously learned.

Remove the positive cables running from the existing lead acid battery bank to the existing inverter/charger(s) already in your coach.

Connect a new house lithium battery bank directly to the inverter/charger already in your coach so only the Li battery bank provides 120vac power to the coach freeing up the lead acid batteries to power only the 12vdc loads.

Remove about half of your existing lead acid batteries.  Since they now power only 12vdc loads, you don’t need as many as you did when they also were powering the high draw inverter to provide 120vac power for your appliances.

Add a Battery-to-Battery charger between the remaining lead acid batteries that are charged by the engine alternator and the new Li house battery.  That will keep the Li battery charged while driving, limit the amp draw to the rating on the BtoB unit to protect your alternator, and properly isolate the Li from the LA batteries.

The existing inverter/charger(s) already in your coach will recharge the Li bank while you are plugged into shore power or while the generator is running.

If you also want solar charging, add one or more solar panels and an MPPT solar charge controller and connect it directly to the Li battery bank.

That is all there is to the topology.  All batteries are recharged automatically while driving and with solar, shore, or by generator power while parked.  The Li batteries power only the inverter(s) to provide 120vac for your appliances, a task for which they are ideally suited.  The remaining lead acid batteries power only the 12vdc pumps, fans, lights, and any 12vdc appliances, a task for which they are ideally suited.

This topology is not only simple, easy, and safe to implement, but it is also very extensible over time.  If you find you need more 120vac power the way you live in your coach, you can simply add a second Li house battery bank, a second inverter/charger, a second Batter-to-Battery charger, and a second MPPT solar controller and solar panels.  

Now you have two totally independent Li house battery banks so there is no risk of mixing two different brands of Li batteries together, which is not recommended, while at the same time you are achieving the objective of increasing the 120vac power available in your coach while boondocking.  Both house battery banks will be automatically charged off the alternator while driving and from solar, shore, or generator power while parked. 

When you do decide to replace all but one of your existing lead acid batteries, just add another Li battery bank, another inverter/charger (or just a charger), another MPPT solar controller, and solar panels.  Connect your 12vdc house loads to this new Li battery and your conversion is complete.

Now, fast forward two years since the first article appeared.  12vdc LiFePO4 batteries have dropped in price to half or less per amp hour than what they were then.They have also increased in capacity from a max of about 100-amp hours then to as much as 400-amp hours in a single battery. The build quality available now can be way better than it was then.  Then low-priced batteries generally meant substandard build quality.  Now build quality is higher across the board and build quality and price are no longer directly related.  

At the same time, the electronic devices used in the conversion of your motorhome or bus to Lithium batteries have also increased in quality and function and have decreased in price.  For example, there now are Battery-to-Battery chargers that also integrate a MPPT solar charge controller so your batteries will be safely and properly recharged while driving both off of the engine alternator and from solar if you have solar panels mounted on the roof.  And, if you size these units correctly for the size of your alternator, they will prevent the alternator from being over-taxed while recharging even large LiFePO4 battery banks.  The cost of these combination BtoB and MPPT charge controllers is now significantly lower than the cost of the two independent charge controllers they replaced from two years ago.  

The combination of these factors means that there is hardly any justification for using lead acid batteries for anything other than keeping one to absorb possible voltage spikes and to provide input to a BtoB charger to charge your Li batteries off your existing alternator safely.  LiFePO4 batteries are now less expensive than lead acid batteries per available amp hour of capacity both in initial cost and certainly in cost over time.  Today’s LiFePO4 batteries and the associated electronics will likely outlive your time with your coach.

One of the important considerations to keep in mind is that LiFePO4 batteries from different manufacturers, or of different capacities, or even from the same manufacturer two years ago and today may not operate safely or properly if directly connected in parallel.  The reason is the battery management systems so important for the health and safety of these batteries have changed, sometimes substantially, over these two years.  

The topology I have outlined here keeps all batteries separated and operating independently so you can mix and match as you wish - new batteries in one bank with old batteries in another, low-capacity batteries in one bank with high-capacity batteries in another, older generation battery management systems in one bank with the latest generation battery management systems in another, and so on.

There are other cases to be made for having two or more independent house battery banks.  One is redundancy.  If you have multiple house battery banks and one fails, you have not lost all your house power, only the portion that failed.  Another benefit of having two or more independent house battery banks is that you can devote each to separate tasks.  For example, some of you will have two inverter/chargers, one for each side of your motorhome or bus.  You can devote one battery bank and its electronics to the driver side (DS) and another to the passenger side (PS) of your motorhome or bus.  If one side fails you can always move the plugins for your appliances over to the other and keep on living as you were, just with reduced power until you can repair the failed side.

If you have a residential refrigerator, you may well want to set up a second or third house battery bank devoted just to powering that refrigerator as it is the highest power draw appliance in your coach.  Losing power to your refrigerator could mean losing a lot of expensive food.

In this article, I will show the implementation of one of today’s high-build quality, high-capacity LiFePO4 batteries directly into this same topology.  It takes only a few properly sized cables and a couple of new electrical components.  You don’t need to change anything in your existing implementation.  

For those of you who have read the previous articles in this series, you know that my Prevost Country Coach conversion came from the factory with a 12vdc house electrical system and a 24vdc chassis system which are completely separate from one another.  So, I have only needed to deal with the 12vdc house system.  

My coach also came with two inverters/chargers, one for each side of the bus.  In my case, these initially were modified sine wave inverters which I replaced with full sine wave Magnum 2800-watt inverters/chargers long before I did the LiFePO4 conversion outlined in this series of articles.  

Step One

In the first article in this series of articles The Advantage of Lithium Batteries for Bus Conversions, I took out half of the lead acid batteries that came in the coach (six 8D AGM batteries) and installed four Lion Energy 100-amp hour 12vdc LiFePO4 batteries wired in parallel to provide a house battery bank to power my 120vac loads with 400 available amp hour of capacity.  I also wired those batteries in parallel to both inverter/chargers, so I had 400-amp hours of capacity for both sides of the coach.  The three remaining lead acid AGM batteries produced about 300 available amp-hours of capacity to handle the coach 12vdc loads.

Step Two

In the second article in this series Best of Both Worlds – Combining Lead-acid and Lithium Batteries in your Bus Conversion RV, I added a second independent house LiFePO4 battery bank by removing one of the three remaining AGM batteries, installing a 300-amp hour LiFePO4 battery from Rebel Battery, and wired these two different house battery banks each to one of the two existing inverter/chargers.  (Note:  see how easy it is to change configuration with this topology!)  

That provided 400-amp hours of available capacity down the driver’s side of the coach and 300-amp hours down the passenger side while still leaving about 200-amp hours of lead acid AGM batteries to handle the 12vdc loads.

Step Three

Here, in this third article in this series, we will walk through how easy it is to now change the configuration again.  EEZ RV Products has recently introduced a new 400-amp hour ruggedized LiFePO4 battery in a welded stainless-steel case with great build quality under the Evergreen Battery name.  I will now remove all but one of the AGM lead acid batteries (leaving it in place only to absorb any voltage spike that could occur from alternator charging), move the 300 Amp hour Rebel Battery to handle only the 12vdc loads and install this EEZ RV Products 400 Amp hour ruggedized unit to handle all the 120vac inverter loads on the passenger side which is where the residential refrigerator is located in this coach.  

By making this change I will wind up with 400 available Amp hours of capacity for the 120vac loads on the driver’s side where the kitchen, microwave, induction cooktop, coffee maker, and 120vac audio/video systems are located, and 400 available Amp hours of capacity for the 120vac loads on the passenger side of the coach where the residential refrigerator, basement refrigerator, and outdoor entertainment systems are located.  The third LiFePO4 300 available Ah battery bank will take over the 12vdc loads like the hydronic heating system, zone system heat exchanger blowers, LED lights, and the over-the-road AC zone system blowers throughout the coach.

On the previous page is a photo of how it looks installed in my Prevost.  The three Renogy MPPT/BtoB chargers are mid-row left.  The inverter/chargers supplying the coach 120vac loads are top row left and right (white boxes).  The inverter/charger for the 300 Ah Rebel Battery Li powering all the house 12vdc loads is bottom row right.  

The battery itself is just above, the center row right.  The 400Ah Lion Energy Li battery bank is in a closet above this battery compartment.  The 400 Ah EEZ RV Li battery bank is the stainless-steel box lower row left.  The one remaining lead acid AGM battery is the lower row center.  The black box upper row center was originally devoted to the 12vdc house loads and is now not used for much.

Note the three circuit breakers just to the right of the Renogy BtoB/MPPT charge controllers.  The heavy red cable coming from behind the black box upper row center and attached to the post on the silver upright piece is coming from the B+ terminal on the alternator.  

The heavy red cable also attached to that post is coming from the B+ on the lead acid battery.  The three circuit breakers supply protected input power to each of the three Renogy BtoB/MPPT charge controllers.  That constitutes the total of what is necessary to keep all three Li battery banks isolated one from another yet properly charged while driving while simultaneously protecting the alternator from any voltage spikes and/or any of the Li batteries drawing too many Amps from the alternator while charging.

Over this two-year period, I oozed into the Lithium battery conversion a little bit at a time while continuing to use the rest of the remaining life in the lead acid batteries I already had.  There simply is no need to take the “all lithium or nothing approach” so widely touted under the banner of “drop-in replacement” these days as noted in my previous article.

This is the simple, easy, safe, cost-effective, and highly flexible way to convert your motorhome or bus over to the many advantages of LiFePO4 batteries.

Editor’s Note: In part two of his article, Jerry will detail why he made the decisions he did and will also talk about what constitutes really good build quality for today’s high-capacity, EEZ RV Products LiFePO4 batteries.