Last month, I shared my latest lithium iron phosphate (LiFePo4 or LFP) battery project. I went into enough detail that I decided to share its installation in this separate article. I mentioned that I would mount the battery in the “cargo area,” which is not specific in a car without a back seat, but also not hard to find in such a small vehicle. 😀 I had planned to put the battery in the trunk, hidden from sight, but opted to mount it behind the front passenger seat for a few reasons, some of which include weight distribution and equipment accessibility.
The trunk seems like a logical place to mount this large battery box. I have a cargo retention rod that stretches across the front of the trunk to keep cargo from sliding into the passenger area that has been very useful. It’s easy to remove in case I need to transport long items that must lay flat. In addition to concealing my cargo, my choice of privacy curtain may also provide a small amount of thermal isolation from a hot interior during the summer months. I had a plan for side-to-side retention of the battery box, but stopped for two rather important reasons.
The most obvious is that the box weighs 82 lbs or 37 kg! I can work with the weight; however, I cannot access both of the box’s retention releases without first removing the parcel shelf and actually climbing into the trunk. I can do that, but would I really want to? Perhaps more important is my need to access the power switches on my amplifiers beneath the trunk floor. This is an infrequent task, but one that needs to be done a few times during a VHF contest weekend. Opening the trunk floor is impossible with the battery box in place, particularly without damaging the car’s composite factory floor panel. And what if I need to access my spare tire as I did during 2025’s Virginia QSO Party?
With the trunk ruled out, I was left with the cargo space that’s above my “rear seat delete.” In 2021, I put my first LFP battery, refrigerator, and inverter on the passenger side to help offset some of my own body weight on the driver’s side. Later, I expanded my tool carrying capacity, which added more weight to the driver’s side. Adding this heavy battery proved to be a great time to swap sides, placing the refrigerator (often empty) and inverter behind the driver’s seat and the battery with tool box behind the front passenger’s seat, resulting in better side-to-side weight distribution.
Placing the battery box on the rear seat delete platform also put its power terminals farther from the cargo retention rod, a safety concern that I had when planning to mount in the trunk. Still, as a precaution, I added a hinged cover to protect the terminals from accidental contact with any cargo that might find itself nearby. My next task was to get 2/0 gauge oxygen-free cable (OFC) from the box to beneath the load floor and connect the existing 12V circuits within the rear seat delete. I cut one-inch notches in the platform and its supporting 2×4 stud, a choice which minimized exposed wire paths.
Once beneath the floor, the 2/0 OFC routes to a safety cut-out switch near the passenger side rear door. Looking at the schematic below, you may wonder why there are identical switches on the same continuous path and so close to each other. The switch on the battery box makes the box itself safe for removal and transport; the switch in the car removes alternator power from the exposed cable ends when the battery is removed. I also consolidated my old ANL fuses and terminal block within a pair of marine rated battery fuse (MRBF) blocks. The MRBF blocks are more compact and help me to avoid stacking lugs while wiring parallel paths.
Next, I removed the outgoing LFP battery and connected its existing circuits to the new wiring. Removing the old battery left more room for running the larger cables without needing to resort to tight bends or stacking of terminal rings. Access to fuses and wire runs is much better with one important exception: Accessing the fuses for troubleshooting or inspection is no longer a quick operation with an 82-lb battery and a 40-lb tool box on that platform! The heavy boxes must be disconnected and removed before the panel can be opened.
Equipment access was one of my critical dilemmas while contemplating where to put the heavy battery. How often do I really need to open the rear seat delete lid to access the fuses beneath? How often do I really need to open the equipment space beneath the trunk or access the spare tire? I only need to access the fuses when there’s a problem, which I hope will be uncommon. However, I need to access the equipment space a few times over each contest weekend. That’s only a few weekends per year, but it’s a common task over those weekends. So, trunk access takes the win!
Oddly enough, since I need to remove the battery box to access and troubleshoot the fuse area, I’ll have to either run the engine or use external power during the rare times that I need to take live measurements in that space. My newly-installed AC-DC charger is looking like a great decision yet again! I’ll use the charger for troubleshooting with shore power or idle the engine if I’m away from a convenient electrical outlet. Otherwise, the primary purpose of the AC-DC charger is to slow-charge over a weekend to balance the LFP battery’s internal cells.
Other than getting a larger vehicle, what other solutions would you suggest? I learn a little more with each configuration change and piece of feedback from curious visitors. Please feel free to share your thoughts.
Power for Days!
Scott
