It's time for an upgrade to the car. My controller is a 48-72V and I already have 6 batteries, so I am maxed out there.
I think the next step is add an additional parallel 6 batteries as "buddy-pairs" to keep the system voltage the same, but double my capacity. If I can ever get my hands on an affordable 144V controller and charger (or just a second 72V charger) I could easily upgrade to 144V later.
I know I will have to upgrade the suspension. I did do a rolling test a while back by setting 6 more batts in the back seat. Suspension was harsh, but the brakes were great, no problems there. That's also right at my GVW, so 12 of these 12V lead blocks is my absolute maximum.
I would like to sink battery boxes down into the frame (er, unibody) of the car. I would do 4 batteries where they are, but lower, in the hatch/spare tire well are. I would sink 4 more straight down in the back seat as that's where the gas tank originally was. And I should be able to fit 4 total batteries under the hood.
Does anyone have suggestions for me about the best way to build battery boxes sunk into the frame? I have limited welding experience, but have plenty of new EV friends who can help me with that.
I also want to make sure to keep the structural integrity of the car. I think that I want to make the "holes" as small as possible. Four of my batteries in a row take up a space of 13" by 28". That easily fits in the footprint of the back seat without cutting into any structural metal folds.
I am imagining cutting a hole in the car with a plasma cutter and then dropping in a pre-built battery box which would have and angle iron lip that would stick out and catch on the the existing metal. In the rear side, that would catch directly on the cross support that the seat belt bolts went into. and I am sure I could extend it just enough to catch, on the front, the structural section of the car body where the metal bends down to form the vertical part at the front of the back seat.
Here is a photo of the back of my car with the existing 4 rear batteries, and the back seat removed.
You can see right in front of the batteries is a structural cross member that I am sure I would want the battery box to mount to.
It's been some time since I removed that gas tank on this car, but I would think that the bolt holes to attach the gas tank could be reused as attachment points for batteries as well. (Not all by themselves of course!)
Any hints or tips on building a box down into the car? Please let me know!