Second Generation Nissan Xterra Forums banner

How-to: 2nd Battery - LiFePO4 in the Rear Storage Tray

23K views 68 replies 20 participants last post by  Kilo Sierra 
#1 · (Edited)
Background

This part of the build is to give some context into who I am, the state of my vehicle, and design decisions I made along the way, mostly uniformed therefor sub optimal. If you want to get to the nitty gritty, jump to the installation post.

So the story begins with me buying a brand new 2015 PRO-4X. The first thing I wanted to get was a light bar. I didn’t like the look of the light boobs on the stock setup. Call me vain, but they just didn’t fit my idea of a big bad Overlander. Before I could get the light bar, I had to get a new rack. A rack that would hold me as I wanted to take pictures from up on the roof. I purchased a DEP Stealth rack, installed it, and then got a 40” light bar.

The light bar presented the challenge: how to power it. As I was a newbie, I had some learning to do to understand why I just couldn’t replace the boobs with the LED bar. The new LED bar takes more current than the system running the boob lights supported. Once I got that all wired up, which involved a fuse block and solenoids behind the dash, it worked like a champ. And I have 11 relays behind the dash just in case I needed them.

But what about running the battery flat? The requirement to preserve the battery so I could start the vehicle became my quest over the past couple of years. I installed a second battery with all of challenges in the engine bay. I installed a pair of Odyssey PC1200MJT AGM batteries. It was a tight fit. I chose the Hell Roaring Battery Isolation Circuit (BIC) to separate the batteries. In order to allow for winching, I had one of those too, I installed a manual Blue Sea battery combiner to bypass the BIC during winch use.

I moved the house circuit to the second battery. The problem was, at the time, I didn’t realize the Xterra alternator/charge control circuit doesn’t work with AGM batteries. At least not well. The result was the AGM batteries were never fully charged. For the life of me, I couldn’t figure out how to get the voltage up over 14 volts for any extended period. My Bully Dog GT was my window into the Xterra charging world and it looked bleak. I purchased an AGM specific battery charger, but that didn’t help when I was on the road. Finally, after months of frustration, I purchased a Rugged Rocks 270 Amp High Output Alternator with a set point of 14.5 volts. Problem seemed to be solved with the voltage consistently running 14+ volts.

Next, solar. I purchased a Victron SmartSolar MPPT 75/10 with Bluetooth. What a nice piece of equipment. I hooked the MPPT up to the second battery and read the charge state of the battery and how much the battery was receiving from the solar panels. This device alone was well worth the price of admission. The Victron products are the best. What it showed me was the battery were not holding the charge very well. Then I added a Dometic refrigerator, setup another set of 4 relays in the back, and relished the wonder of having milk on my overland trips.

All was not well in the dual battery kingdom. The BIC wasn’t doing its job well from what I could determine. I assumed I had burned it up. My next solution was to replace the BIC and the Blue Sea battery combiner with a Blue Sea ML-ACR automatic charging relay with manual control. Cool. It worked great and could handle all the current when winching. Along this time, I noticed the battery was not holding a charge for very long. Looks like I had ruined the battery over time through deep discharge and not filling the battery up all the way. It was time for a new battery. But why go with something as simple as replacing a battery? Nope, it was time for a change in battery technology. And battery placement. The adventure begins.
 
See less See more
#2 · (Edited)
Investigation

Where to start? I wanted to move the battery out of the engine bay. Chris H. had a big heat problem with his batteries and the engine bay is a harsh hot space not well suited for more stuff. Moving the 2nd battery to the back is what most people do and then build a storage system around the batteries.

I always thought the rear storage tray in the back was useless space. I kept some earthquake clothes in there, but it is a space that isn’t accessible when I’m on the road. What happens if I add a drawer system? No access at all. The challenge is the space is thin only about 4” high. I thought about the Tesla design using a large quantity of 18650 Li Ion batteries in the undercarriage. Perhaps I could make a battery block to fit in the rear storage tray. I talked with a friend of mine who worked with batteries and he said the biggest problem is connecting the batteries together. The best way is to spot weld the bus bars on the batteries rather than solder them together. I explored various other options and finally decided to abandon the idea of using 18650 batteries.

This same friend told me the best battery to use is a Lithium Iron Phosphate battery. These battery cells are 3.2 volts and are much safer than standard Lithium Ion batteries. Good to know! The other aspect of LiFePO batteries or all Lithium Ion batteries for that matter is available power. A typical lead acid battery has about half of the rated amp hours available. You can’t draw down the voltage of a lead acid battery much lower than 50% capacity. Yes, deep cycle batteries are better, but they are still do not allow for the harvesting of the total capacity. Lithium Ion batteries on the other hand provide virtually all the of the rated amp hours. This means that if a Lead Acid (this includes AGM batteries) has a 100Ah capacity you would need two to match the same available power from a single 100Ah Lithium battery. Lithium Ion batteries have another benefit: much higher available cycles. Lithium batteries last longer as a result and that is why they are used in automobiles where the batteries are discharged and recharged everyday. One major drawback of LiFePO is they are not suitable for vehicle starting. Not a problem in my case as I’ll continue to use the standard battery.

There is a new technology named Lead Crystal batteries, which get around most of the problems with traditional lead acid batteries and are used by Andrew White. In this case, though, they are the wrong form factor for what I want.

I came across Will Prowse on youtube. His web site www.mobile-solarpower.com turned out a wealth of information. I found this article to be very helpful: https://www.mobile-solarpower.com/design-your-own-12v-lifepo4-system.html Then there was his youtube video showing him building a battery pack:



which provided much needed information on the whole project of building a LiFePO battery solution. The size and shape of the cells got me to thinking. Instead of making them into a block, why not arrange them into to two stacks of two cells. I found that I could make a 100Ah battery that would easily fit in the rear storage tray! What!!! I now had a solution for which batteries to use in the solution.

Another person who has been helpful in my education is Andrew White’s youtube channel:

https://www.youtube.com/user/4xforum

@ChrisHaynesUSA posted a set of links to Andrew’s videos which filled in my knowledge gaps such as this one on why you need a charge controller:



Boy do I wish I had this guy before I got into my project. It would have saved a lot of wasted effort. Finally, here is another video that helped me understand the whole premise of building a system that is wholly separated from the vehicles standard wiring thus avoiding potential warranty issues:



Using information from Andrew and Will, I decided to use the Renogy 40A DC/DC charger and my Victron MPPT controller. This combination would be just fine for my purposes. My inverter is only 400W not the 1000 to 2000 behemoths used on some RV solutions. This really helps reduce the overall current requirements for the solution. I was now ready to start designing.
 
#3 · (Edited)
Design

The core of my design are the prismatic LiFePO batteries. Here is one 100Ah cell:



I ordered these from China. They cost $64 per cell plus shipping and tariffs for a total of $85 each. Total cost on the batteries ~$340 for 100Ah of glory!

The overall wiring from the back to the front:



The top picture is the cabling from the battery to the DC/DC converter. The second drawing shows the interconnection in the rear storage tray itself.



First the BMS, which I got off ebay:



Cost ~$35

For the charger, I chose the Renology 40A DC/DC Battery Charger:



Cost ~ $210

For the MPPT solar charger, I chose the Victron MPPT 75/10 with blue tooth charge controller:



Cost ~ $125

All pretty simple really. The challenge is all the bloody wiring required. I used jumper cables for the #4 and #6 wires running from the engine compartment back to the rear storage tray and from the rear storage tray back to the front cabin as they are less expensive than buying the wire itself. I have eight left over battery clamps.
 
#4 · (Edited)
Installation - Part 1

Now the hard part, which isn’t trivial by any account. Compared to moving the Power Steering pump, fabricating a new battery tray, and the various brackets needed for installing a second battery in the engine compartment, putting the battery in the rear storage tray is a piece of cake. Couldn’t be simpler! The items that stopped the project were usually wire or connectors.

Luckily, I leveraged the work done for the original 2nd battery installation. All wiring under the dash and in the back would need to be powered from the 2nd battery in the rear storage tray. A PIA, but not insurmountable.

I have the wire cutters, strippers, terminations, wire crimpers, and other tools. The consumables were mostly the terminals, wire ties, and silicon sealant.

Take out the rear tray.



I took the rear tray and put it on a table to layout the parts and get them all situated in the tray.



3M VHB tape is used to hold the batteries together and, once the bus bars are installed, hold the batteries to the rear storage tray.



The wonderful new is the rear storage tray is heavy plastic which is a perfect electrical insulator. The battery terminals are place on the outside to prevent anything from inadvertently hitting them.





The Renogy DC/DC charger had bolt holes, so it was bolted to the rear storage tray.



The tray is removable so the wires must be disconnectable. Anderson Powerpole connectors are used to handle the large current running through the wires. The fuse from the front 2nd battery was used to protect the battery from any shorts. The closer to the battery the better! The BMS was wired and taped to the front of the rear storage tray.



I didn’t install the MPPT charge controller at this time, but now is the right time to get it installed.

An access hole was cut in the body of the car to allow the cables to go from the outside to the inside. This could be cleaner holes and gromets for each cable. I chose to cut a big hole, clean up the edges, paint them to prevent rust, line the edges with door trim, and, later, use flex tape and silicon calking to seal and protect the opening.






The rear power distribution, four relays, the 400W inverter, and the compressor is in the passenger wheel well. The challenge is to get the cable into that space. Turns out if you remove the Drafter duct, there is direct access to the wall to drill through to the underside. That is tricky. The hardest part is getting access to cut or drill holes!





For the solar cables, they are run from the rear storage tray to the passenger step. First drill the holes in the rear step.



Next drill holes for the cables to go from the step over to the other side and into the rear storage tray:



This part of the body is triple thick sheet metal. Spray the edges to prevent rust. I don’t have grommets to protect the cable and the edges are sharp! Taking thick vinyl tubing, cutting, rolling, and sliding it in worked just fine to protect the cable. Those are not coming out:

 
#5 · (Edited)
Installation - Part 2

The cable from the main battery back to the rear storage tray is protected by a fuse, runs down the wheel well/firewall, along the frame, and into the rear storage tray:









The cable from the rear storage tray to the cabin runs up the frame, along the wheel well, and into the cabin just below the glovebox and high up on the carpet. Two gromets protect the cable from the sharp edges of the metal body.



To protect the cables from chafing on the sharp metal, door protector molding is installed around the hole, flex tape taped to the underside, and generous amounts of silicon calking is applied.





Configuring the DC/DC converter wasn’t as easy as I had hoped. The manual has a misprint on page 22. The final configuration after giving Renogy a call was:

  • S1 – OFF
  • S2 – ON
  • S3 – ON
  • S4 – ON
  • S5 – OFF
The charge parameters are the ideal absorption voltage of 14.6V and the float voltage at 13.5V. One difference from Lead Acid and Lithium Ion is Lithium Ion does not require a float voltage and really doesn’t like them Setting the float voltage lower than the nominal voltage prevents the batteries from being ‘trickle’ charged which is why the DC/DC charger must be designed with Lithium Ion in mind.

Snug as a bug in a rug! About the same power potential as @ChrisHaynesUSA setup for the house side. I still have the battery for the vehicle under the hood though. Great use for previously unused space and now I have plenty of power ?️‍♂

 
#6 ·
Afterthoughts

What a project. I will have more information as I go along on what worked as expected, what worked beyond expectations, what should be done differently, what didn’t work as expected. During the research, several products originally designed for Lead Acid are being reworked to support LiFePO4 which might provide a more turnkey solution.
 
#13 ·
Very nice setup. I'm in the process of planning a dual battery install myself to the right of my cargo drawers using a G24VMAX battery and CTEK DC-DC Charger but I also have that storage area that is just dead space under my drawers so that gives some ideas. Do you have a link for those batteries? I searched for them on the fleabay but only found 50ah 3v ones.
 
#20 ·
Awesome write up Hank! This is going on the never ending to do list. I don't need the power yet but in time I will and I love this set up. Super clean without the need for two in the engine bay or taking up endless space in the back.

What do you think four of those batteries weigh?

Sub'd to see your updates~

Lucas
 
#24 ·
Yes, I am a HAM. Like 4x4, I never saw a benefit until I met some people who were having a ball. In the case of 4x4, a group of friends were going up to Death Valley National Park and wheeling around. Which led me to an Xterra, which led me to here, which led me to HAM.

@ChrisHaynesUSA insisted participants in outings have a HAM license. I must say HAM is exponentially better than CB in terms of range and clarity. A must have safety skill. Getting a license is easy: go to Online Ham Practice My son spent a few days, took the test, and passed! I studied when I was down with a broken ankle and now have my general license. You only need the technician license unless you want to really geek out. For everything useful, technician license is all you need. Easy peasy
 
#25 ·
While I am here, I have an update on this project:

I installed a Bioenno 10 A AC/DC LiFePO4 charger:



Then I ordered and installed an AC plug port:



Here is the finished installation.



Now I have the ability to charge from the alternator, solar panels, and AC. Sweet...

The next idea is to mount my flexible solar panels on top of my Roof Top Tent. Waiting for the white Flex Seal now :cool:
 
#27 ·
Nworker. I have been rereading your thread for a few days now, and watching the linked youtube videos. I think you have cracked the code on the Xterra battery situation. I REALLY like how you were able to find a deep cycle battery solution that fit inside the cargo tray!!!

At this point I am tracking pretty well on the components you wired up inside the tray (batteries, DC-DC charger, controller, etc). I need some help understanding how you were able to connect this battery system to the devices that need power (light bar, air compressor, fridge). You mentioned relay boxes a couple of times in your intro. You said that you have "11 relays in the front" and "4 relays in the back". I'm guessing that this is a junction box of some kind with fuses and receptacles. Do you have any pictures of those boxes? Do you have any other references that can help me learn how to do that?

The electrical situation in my truck is about to evolve fast (wife wants a fridge, winch bumper on its way, need lights). So, I really appreciate your write up, and any other references that will help me up the learning curve.
 
#30 ·
Nworker. I have been rereading your thread for a few days now, and watching the linked youtube videos. I think you have cracked the code on the Xterra battery situation. I REALLY like how you were able to find a deep cycle battery solution that fit inside the cargo tray!!!
Thank you. I have gotten so much from others on how to outfit my rig. It is great to give back to the community.

You mentioned relay boxes a couple of times in your intro. You said that you have "11 relays in the front" and "4 relays in the back". I'm guessing that this is a junction box of some kind with fuses and receptacles. Do you have any pictures of those boxes? Do you have any other references that can help me learn how to do that?
Here is what I followed for the front wiring setup. It was a huge project. My neighbors thought I was crazy taking apart my brandy new rig:


Here is the setup for the back area.


I replaced removed two of the relays and went directly to the rocker switches, which can handle up to 20AMPS, to reduce battery drain for switching. I have the compressor and the inverter on relays. The rear lights and refer are directly switched.
 
#28 ·
Found a battery source for 1$/aH in Alameda. I bought a 100aH LiFe pack sans BMS. Going to put that in the tray probably and another one on the trailer.



Sent from my iPhone using Tapatalk Pro
 
#29 ·
Text Floor plan Line Diagram Plan


I found this schematic from ALKELI in his thread about relays. It is all starting to make sense now.

If I got this correct, your LiFePo cell in the back is connected to the starter battery + alternator via a solenoid of some kind for charging when the vehicle is on (perhaps the DCDC charger does this switching/isolation for you?). Then you ran power from the AUX battery back to the front relay box to power your front lights and ham radio. You also ran power from the AUX battery to the rear relay box to power your fridge and inverter. Do I have that right?

My next question is about your BMS. I gathered from the Will Prowse video is that this device redirects power to certain cells in the battery system to "equalize" each cell and ensure that they have equal charge. Prowse said that this was only necessary every 3-6 months. Did you chose to leave it on all the time?

It would really help me out to see how you configured your box in the rear. The guys in the 4xOverland video built a custom box that bolted to cargo barrier where the rear seats used to be. I need to keep my rear seats in place, so I could use some ideas about how to efficiently get this done in our truck space.
 
#31 ·
If I got this correct, your LiFePo cell in the back is connected to the starter battery + alternator via a solenoid of some kind for charging when the vehicle is on (perhaps the DCDC charger does this switching/isolation for you?).
From the battery, two wires (+ and -) run to the back where they connect to the input of the DC/DC charger. I don't have a relay on that circuit. I have the run fused right at the battery in the engine bay.

Then you ran power from the AUX battery back to the front relay box to power your front lights and ham radio. You also ran power from the AUX battery to the rear relay box to power your fridge and inverter. Do I have that right?
Yes you have this right.

My next question is about your BMS. I gathered from the Will Prowse video is that this device redirects power to certain cells in the battery system to "equalize" each cell and ensure that they have equal charge. Prowse said that this was only necessary every 3-6 months. Did you chose to leave it on all the time?
The BMS has balancing built in and is performing cell balancing all the time. There is no need to perform battery balancing with this setup. In the past, hackers would balance the batteries, which were usually used batteries, but not always, and then charge them with a charger being careful not to over charge, over discharge, or generally use the batteries in an unsafe way. The BMS I'm using takes care of all but the temperature sensing.

It would really help me out to see how you configured your box in the rear. The guys in the 4xOverland video built a custom box that bolted to cargo barrier where the rear seats used to be. I need to keep my rear seats in place, so I could use some ideas about how to efficiently get this done in our truck space.

If the write up on my build page isn't sufficient to give you an idea on how to mount the switches, relays, compressor, and inverter in the wheel well space, check out this thread with the rear passenger panel removed showing the void in which people install a small air compressor:


 
#33 ·
Okay the march continues. This morning I mounted two 100W solar panels to the top of the Roof Top Tent.



I cleaned the back of the panels and roof top with alcohol. Then I prepped the surface with adhesive promoter:



To attach the panels to the roof, I chose Scotch Mount Moulding Tape:



I aligned and put down the panels. One the leading edge I used Flex Tape, I swear the stickiest stuff on the planet.

 
#35 ·
Okay the march continues. This morning I mounted two 100W solar panels to the top of the Roof Top Tent.



I cleaned the back of the panels and roof top with alcohol. Then I prepped the surface with adhesive promoter:



To attach the panels to the roof, I chose Scotch Mount Moulding Tape:



I aligned and put down the panels. One the leading edge I used Flex Tape, I swear the stickiest stuff on the planet.

That is slick AF! Great job! Which panels did you use? I like the idea of the flexible ones.
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top