In any case, it will bring the weight of the car to just about where I'd like to have it and once I've registered the car as it is, I can always swap the batteries for better ones later as they improve over time. I will probably need to construct a small battery box in the front as well. I'm thinking of placing the 40 Ah cells (35 kg of them) in the front and the 60 Ah cells (65 kg) in the back. That should give me a pretty nice weight distribution and since I've taken out around 60 kg from the back anyway with the fuel tank, spare tire and exhaust, I might even get lucky and not lose any seats. We'll see.
The two packs will be connected in parallel (25s2p, if you will) and I'm quite confident that they will balance the difference in capacity by themselves, both during charge and discharge. In any case, it will be impossible for them to be at a different voltage. I'm also sure the total voltage will immediately show if there's a problem with any of the cells in either pack, since it will start sucking juice from the other pack. It's not quite as sure shot as with a simple single series pack, but I think it will do for now. These two packs may see a new life later on in two separate motorcycles, if and when the car gets bigger cells.
In other news I solved the issue of pack negative leaking into the car chassis via Alltrax AXE7245 throttle input 2. I did this by taking the pack voltage down to 12 volts using a power supply and from there to 5 volts using a little DC to DC converter. This way I don't have to connect the 5 volts negative to the chassis at any point. For whatever reason my TPS kept on giving 1.2 volts on zero throttle instead of the 0.65V before, but that got solved with a new curve from picoamps.de. They came through again in a day or so. Very good service.
With the ground leak problem solved and a new curve in the controller I was able to take the car for a little spin in our yard. Well, not a spin really, since there's no room to spin, but some motion back and forth anyway. Looks like my reverse light wasn't working though. Probably just the reverse detector plug got loose again from the transmission. It's missing the clip to keep in place properly.
Almost forgot. The hissing sound that the car makes comes from a rather loud blower I also installed. I don't expect the motor to heat up too much, but the blower pushing filtered air into the motor should help to keep it clean inside and also blow out any carbon dust from the brushes. I don't think I'll do anything about the noise. It's not a very pleasent one, but I reckon it's not a bad idea for the vehicle to make some noise audible at low speeds to alert pedestrians, which might otherwise be taken by quite a surprise.