DriveEV Logo
JeepEV: Electric Vehicle Conversion Project
Battery Boxes/ Racks

     Now the big challenge: How to safely fit and secure 20 large, heavy batteries on the Jeep. The batteries will be secured in large battery boxes which will be welded to the vehicle's frame. The first step was to identify possible battery box locations. The engine (now Motor) compartment and under the trunk floor were the largest and most practical spaces for the main battery boxes. - more later... -

Front Battery Boxes Fabrication and Installation:

     The Engine compartment in the Cherokee is big and has room to hold two separate battery boxes. It is important to note that the front battery boxes are actaully more like "racks", since they aren't fully enclosed all the way around. Instead both front racks have a tray style top and bottom, and open sides.

Front Battery Rack #1:

     The first battery box sits above the electric motor. This box holds 4 of the 20 batteries, and was made using "L" channel, flat, and square tube shaped steel. Due to the unusual way this box is mounted, we built it from scratch in the garage. The first thing we did was measured the space. We decided we would place two rows of two batteries in the space over the Motor, with the length of the batteries parallel to the firewall of the Jeep. Next we cut four pieces of "L" channel with 45 degree ends, so that the "L" channel would form the base of the rack/box. We laid the four pieces together to verify that once welded, the four batteries would fit.

Battery Boxes Page Photo
The rack base is tested for a fit of the batteries.
using a wood model battery I made.

     Next we Spot welded the bottom of the rack together. However, we made an error somewhere and the rack was literally about 1/16" to small all the way around. Doh! Back to square one. The error in size was just something we couldn't work around without having to rebuild the rack bottom, so we did. This time we left about 1/4" of room all the way around, so the batteries fit freely.

Battery Boxes Page Photo
The first rack as compared to the second (good) rack.
It's amazing what a 1/16" error can cause...

     After setting the errored battery box tray out of our way, we began to finish off the bottom tray of the first front battery rack. Using three pieces of flat steel welded together, we created a cross that we then welded to the bottom of the rack. This adds support to the bottom of the tray and will also provide mounting points for other components. Next, we cut a piece of square tubing and a piece of "L" channel to the length of the side of the tray, and welded them on. The square tubing attached to the bottom of the tray to provide depth, and the "L" channel then welded onto the square tubing to provide a mount.

Battery Boxes Page Photo Battery Boxes Page Photo Battery Boxes Page Photo
The first battery box tray with cross metal welded in
place and the passenger side mounting "tab" welded on.

     The driver's side of the battery rack utilizes the same kind of mounts as the passenger side. However, instead of using one long piece of "L" channel, we cut and used two small sections instead. These were welded to a length of square tubing which was then welded to the bottom tray. One of the "L" sections on the driver's side will mount to the electric motor mount, while the other section will mount to the old driver's side engine mount perch.

Battery Boxes Page Photo
Two sections of "L" channel are welded on to form
the driver's side mounts.

     After the mounts were finished on the rack itself, we prepared the frame of the Jeep so they could mount to it. We drilled two holes in the passenger side mount, and one hole in the rear driver's side mount on a drill-press. Next, we set the battery rack on the frame where it was to go, and drilled the holes into the frame rails. The holes were then drilled one size larger to accept 3/8" size Riv-Nuts. Riv-nuts are basically a rivet with thread in it. Using the riv-nuts gave us new bolt holes in the frame that are nce and solid. For the front driver's side mount we were able to make use of an exsisting, threaded hole in the old engine mount perch.

Battery Boxes Page Photo Battery Boxes Page Photo
Bolt holes are drilled in the rack and Riv-Nuts are
pressed into the frame. It's solidly mounted!

Front Battery Rack #2:

     The second front battery rack sits in front of battery rack #1, and just behind the radiator area. This rack is identical in size and shape to battery rack #1, and also holds 4 batteries. The difference between it and rack one is the way it is mounted to the Jeep's frame.

     The passenger side mount of battery rack #2 is similar to that of Rack #1. To make the mount we used a section of "L" channel cut to the size of the rack. The "L" channel was then welded directly to the side of the lower tray, and no square tubing was used. A second mount was made from "L" channel to support the driver's side rear corner of the rack. This mount was also welded directly to the lower tray, and will make use of an existing hole in the old driver's side engine mount perch.

Battery Boxes Page Photo Battery Boxes Page Photo
Two pieces of "L" channel are welded to the lower tray
to provide the passenger and rear-driver's side mounts.

     In addition to the two mounting points listed above, battery rack #2 needed more support in the front, mainly on the driver's side. We were unable to simply make a mount attached to that corner because the Jeep's steering gear box is mounted to the frame in that area, and gets in the way. Instead, we decided to make a mount that would mount to the Jeep's frame in front of the steering gear box. There was already an existing piece of metal which spans across from one frame rail to the other and used to be a plate that the radiator sat on. This piece of metal, however, isn't very strong and wasn't removable (as it is welded in place). So, we decided to weld a piece of "L" channel all the way across the front side of the battery tray. This "L" channel was cut longer than the length of the tray so it would rest across the tops of both frame rails and on the old radiator support metal piece. For that to work, we first had to grind off the flange that was bent into the end of the old radiator support piece

Battery Boxes Page Photo
The old radiator support piece of metal that ran across
the front of the engine compartment was grinded flat.

     Next, we welded a small piece of flat steel to the end of the "L" channel to double it's width in the area that sat over the frame rail. This new flat tab provided a spot where it can be bolted to the frame rail.

Battery Boxes Page Photo Battery Boxes Page Photo
The new front mount is made out of "L" channel
and spans across the front of the lower tray.

Mid Battery Boxes Fabrication and Installation:

     The mid battery boxes were fabricated and installed after the front trays and rear box had already been completed. The mid battery boxes make use of the free space under the rear seat, on either side of the rear driveshaft. Each holds one battery. The idea of utilizing the space under the rear seat for batteries was played around with back in the planning stages of the conversion. However, suspending boxes under the rear seat was something which I only wanted to do if we ran out of space in the engine (now motor) compartment and/or the trunk. After packing 8 batteries in the motor compartment under the hood and (as you'll read about below) 9 batteries in the box under the trunk floor, I still needed to fit in 3 more. So the mid boxes and what I call Box #4 (also mentioned below) were created.

     The first step to installing the boxes under the rear seat was to actually make the boxes. Earlier in the project, I had had the sheet metal shop construct a larger box for the Jeep which was capable of holding 3 batteries. After finding no practical use for this box, I cut it into thirds. The middle section was then set aside, but either end section (each now missing a side) were used. I had the sheet metal shop stamp out two new sides needed to finish off the two cut ends of the large box into smaller boxes. Also, I decided to cut a section out of the boxes in their length dimension. This cut-out section would make the boxes about 2" shorter in length when welded back together. The purpose for shortening them was to make them as tight as possible (while still leaving a little space all around the battery) so that it would be easier to fit them in the limited space under the rear seat. The boxes were then ground around the seams with the electric grinder and re-welded together. They weren't pretty before being painted, but it saves some money. I learned that sheet metal this thick isn't that cheap, so it was good I was able to reuse what I already had.

Battery Boxes Page Photo Battery Boxes Page Photo Battery Boxes Page Photo
Under the rear seat before any modification.
Also, two new boxes are made for use under the seat.

     After the boxes were made, It was time to cut holes for them in the metal floor panel under the rear seat. I used a drill to mark the corners and provide a hole for the sawzall to begin its cut. Then using the sawzall, I cut the rectangular hole required for the boxes on either side of the center "hump" which is there to provide space for the rear driveshaft under the vehicle. After the initial holes were cut for the boxes, I had to use a combonation of a jigsaw and the electric grinder to enlarge the holes to just the correct size. Also, while cutting, I had to be careful of the parking brake lines (which are modified during this time (see this page < under construction >).

Battery Boxes Page Photo
The holes for each battery box are cut in the floor
under the rear seat of the Jeep.

     Once the holes were the correct size, we ground down the surfaces around the openings to remove the paint and undercoating so the welds would work properly. Then we placed a jack under one box to hold it in place and tack welded it in. Next, we did the same for the other box. After verifying that the boxes were in the correct position, we did a final weld on them, using "L" channel where necessary to strengthen the connection between the boxes and the body of the vehicle.

Battery Boxes Page Photo Battery Boxes Page Photo
The boxes are welded into position.

     The last step was to paint the insides and outside of both boxes to prevent rust. I chose silver for the insides and flat black for the outsides. The two under seat battery boxes hold two of the 20 traction pack batteries.

Battery Boxes Page Photo Battery Boxes Page Photo Battery Boxes Page Photo
The boxes are painted and the seat is folded into
its normal position.

Rear Battery Boxes Fabrication and Installation:

     The Jeep's trunk used to have the gas tank beneath it. With the gas tank now gone for good, there is alot of empty space under the rear of the Jeep. Unfortunately, the rear axle shock absorbers mount to a weird shaped cross member under the trunk, thus creating a weird shaped area to work with. But first the trunk floor had to go. The first step was to remove the carpet and padding, and fold it back out of the way. Next, I drilled small holes up through the bottom, to mark the edges of where the cut needed to be made.

Battery Boxes Page Photo Battery Boxes Page Photo
The trunk carpet is removed and holes are
drilled around the perimeter of the area to be cut out.

     Once the perimeter of the area to be cut out was marked with the holes, I took a sawzall and slowly cut out the floor. It was amazing how easy the trunk floor metal cut out, but it is pretty thin metal. As you'll see in the pictures, I left the shock absorbers' cross-member intact. I had contemplated remounting the driver's side shock absorber to the front of the rear axle tube, just as the right side one is mounted. However, the effort and expense involved to have someone cutoff and remount the shock mount to the axle tube hardly seems worth it. So, the shocks stayed where they were.

Battery Boxes Page Photo Battery Boxes Page Photo
The trunk floor is slowly cut out from the top
Note The cut went around the shock crossmember.

     The rear battery box to fill the now empty space under the trunk floor was made out of heavy gauge sheet metal. The box was actually fabricated by a sheet metal shop in Austin, and came as a three sided box made of one piece of metal, and two sides. Mark from Austin EV group was nice enough to weld the other two sides on the box, which saved on the cost of the sheet metal shop's fabrication. We now had a nice new, shiny, and rather heavy sheet metal box.

     The first step in altering the new box to fit under the Jeep's trunk floor was to shape the box to fit in the odd shaped space I was now left with under the trunk floor. The box had to curve around the shock absorber's cross member. To do this, we traced then cut the curved shape out of the sides and bottom of the box. The next step actually took place before the front and back sides had been welded on to the box by Mark and it was to bend the front side to the now strange contour of the front of the box. This may sound easy, but sheet metal this thick is very hard to bend. Mark and Chris from Austin EV group used a big mallet to kindly convince the metal that it really did want to bend to the contour of the box. Once it had been "formed", it was then welded to the front of the box.

     The next modification was to cut rectangular sections out of the top edges of either side of the box. This was necessary because the "frame rails" in the Jeep are not straight, instead they curve inwards some as they approach the rear wheel wells.

Battery Boxes Page Photo Battery Boxes Page Photo Battery Boxes Page Photo
The under-trunk floor battery box is made of sheet metal and
formed to fit in the oddly shaped space under the trunk floor.

     Now that the rear battery box was shaped correctly, it was time for the installation. First we slid the box under the rear of the Jeep. Next we put the box on top of a floor jack, so we could easily maneuver it as we lifted it up into position (remember, by this point the box is nice and bulky.) The next step was to slowly raise the box with the floor jack. While doing so, we attempted to align it up properly. The box ended up getting caught up in a few corners, so required us to take the electric grinder to the Jeep to enlarge the hole slightly in a few places. once we lifted the box into it's final position, we tack welded it into place and removed the floor jack. After checking once again for the proper fit, we used the welder to finally secure the box in place. The box was mainly welded to the bottoms of both "frame rails" (not the " " because this is a uni-body vehicle) by using "L" channel. it was also welded to the inside sides of the "frame rails." We did end up removing the passenger side tire to be able to have easier access to the location for the welds.

Battery Boxes Page Photo Battery Boxes Page Photo Battery Boxes Page Photo
The rear under-trunk floor battery box is lifted and
maneuvered into place and welded in.

     After we finished welding in the box, Mark jumped in it a few times and declared it seemed nice and secure. We then painted all the outward facing sides of the box with primer and flat black paint. The rear battery box holds 9 of the 20 traction pack batteries.

Battery Boxes Page Photo Battery Boxes Page Photo
The rear under-trunk floor battery box's underside is painted after welding.

     Rear battery box update: I discovered after driving the Jeep during the test runs that the rear battery box needed to be altered. The problem was that as the suspension flexed, the front most corner of the battery box would hit the rear axle near the differential. This of course would cause a loud "Thunk" at times, which was both annoying and bad for the box. What was interesting was that the rear box, which we had designed to fit perfectly into the available space and NOT interfer with the axle, interfered anyways. This happened due to the sight axle movement in the rearward direction as load is applied to the leaf springs. This movement, which we originally didn't plan enough for, caused the axle to move just close enough to the box to interfer with it.

     The fix was to cut out the corner of the battery box and weld a flat plate over the cut-out hole (effectively eliminating the sharp corner which would hit the axle). Luckily there was extra room in the battery box to account for this slight area loss. We used a plasma cutter (perhaps the coolest tool used in this project) to cut out the corner of the box, leaving a triangular hole.

Battery Boxes Page Photo Battery Boxes Page Photo
Battery Boxes Page Photo Battery Boxes Page Photo
The rear battery box's front most corner is cut with a
plasma cutter, leaving a triangular hole.

     After the hole was cut with the plasma cutter and the metal had cooled (plasma is incredibly hot), it was time to patch the hole. I still had scrap metal from the battery box left over, from which we cut a triangular piece with the plasma cutter. Next we positioned the piece over the hole and welded it in place. After patching the box up, I decided to go ahead and fiberglass the inside of it. The fiberglass is electrically insulated, protects the metal from rusting, doesn't absorb battery acids, and cleans up easily. I'll go into details about the fiberglassing procedure later...

Battery Boxes Page Photo Battery Boxes Page Photo Battery Boxes Page Photo
The triangular patch is welded in place then the
inside of the box is fiberglassed for protection.

Battery Box #4 (Tiny Box in trunk):

     With eight batteries in the front of the Jeep, two under the rear seat, and nine under the trunk floor, I still had one last battery to place. It was really not critical to install the remaining battery, but I figured that since I had bought twenty batteries, I should use twenty batteries. Plus, the higher the voltage of the battery pack, the better performance it provides, so I wanted to use a pack with the highest voltage possible. The big problem was where to put the twentieth battery? The engine compartment was already full (except for the space I was leaving open for air conditioning components). After thinking about it, I decided the only place I still had enough room was the trunk. The Cherokee's trunk has an cove like area off to each side behind the rear wheel wells. The passenger side cove is filled by the battery charger, so I decided to make use of the cove on the driver's side.

     In the way, however, was a "hump" which protruded into the trunk to allow sufficient space for the gas filler tube to clear the trunk floor at a diagonal. I needed to remove this "hump" to be able to place the battery as close to the wall as possible (to minimize how far it sticks out into the trunk). To remove it, I used a sawzall and an electric grinder with cut-off wheel. Luckily it was made of fairly thin metal which was easy to cut. The only problem was the plaster that was use to help seal all the seams; lets just say that grinding into the stuff produced a less than desireable smell.

Battery Boxes Page Photo Battery Boxes Page Photo Battery Boxes Page Photo
The protruding gas filler "hump" in the driver's
side cove of the trunk is removed with a sawzall.

     Once the space was cleared, a battery box was made. This small box was made out of the same type of sheet metal used for the mid battery boxes. It was a piece of flat sheet metal which was folded up to create two sides by a sheet metal shop. We welded the other two sides on the box (rather than pay the shop to do it.) Once welded together, I cut two holes in the bottom of the box so the liquid tight conduit could mount to it. Next I primed and painted the box. I chose to use the same silver color used on the front battery racks for the small box. Lastly, riv-nuts were installed in the trunk floor and the box was bolted to them to hold it in place.

Battery Boxes Page Photo Battery Boxes Page Photo Battery Boxes Page Photo
The small box is welded together, painted, and
bolted to the trunk floor with bolts and riv-nuts.

Check out the Battery Page for information and pictures of
how the batteries are installed in the battery racks/boxes.

Remember, More photos are in the Photo Gallery!