This is a great discussion topic, and thank you for the detailed pictures. So from what I can see, just above the bottom plate are the details of the cooling system, starting with the water intake/outlet manifold in black, then the black piping going into the heat exchangers that look like aluminum plates with striations on top; where as the iX (bottom picture) has 10 heat exchanger plates below the shown main outbound and inbound pipes, and one on top, corresponding to the 11 battery modules, the i4 has 4 large heat exchangers spanning the whole width plus one smaller on the far right, below the main pipes, and two smaller heat exchangers on top. Once the stack is put together, the whole piping seems to fit between the battery modules for the iX and in the "transmission" tunnel for the i4, above the battery modules, with pipes going down to the heat exchangers, between the battery modules, in the trough visible between said modules in the layer above the cooling layer. Above the modules as represented here is the electrical distribution, which connect all the modules to the control module top right, sitting in the front "bump" in the top plate.
The good news is that contrary to AMG's early depiction of their battery pack and possibly Tesla (one may think due to their round form factor, similar to AMG's, compared to the flat BMW battery cells), the water cooling system seems to be completely sealed off instead off "flooding" the whole battery pack around the modules; I think this would promote a better control of the water flow, and the water piping also ensures that the cool water reaches all the battery packs at once and the heated water gets collected again from all the packs at once; the downside is that the water has to be kept very clean, as any debris may clog one of the pipes and allow one of the modules to overheat. I have no doubt that the individual modules are monitored to detect such an issue, and that there are leak detectors in case any of the piping should fail. So while the battery physical build-up is certainly less "symmetrical" in the i4, I don't think that the cooling system would be any less efficient assuming the piping is designed appropriately (and it's a fair assumption, these are German engineers after all, they are known for their OC attention to details). I do like the controlled, positive pressure & flow control, i might say that's typical of German Engineering. I'm sure it is costlier than a "flooding" approach, and time will tell whether the added complexity will pay off reliability-wise, since more complexity unfortunately results in more potential for component failure. BMW's ICE reliability has been less than stellar, I actually swore never to own one again after my 135i (lovely car when I had it but it spent 10% of the time at the dealer's), but I'm taking a chance that they'll redeem themselves with the simpler EV technology, and the Engineering cautiousness they have shown so far.
Another conclusion is that if you own the car (I put a deposit for an i4 M50), and an warning message appears regarding a leakage in the battery cooling system, or if suspicious liquids drip down below the car (other than A/C condensation, of course), I would not wait to bring the car to the dealer during the battery warranty period (the i3 has 8 years/100,000 miles, with a guaranteed 70% capacity by the end of the period, so I would not expect anything less for the i4 or iX), and to a qualified mechanic afterwards.
An i3 owner did a great job verifying his degradation over the 3 years/70,000 miles he owned an i3 at
BMW i3 Long Term Battery Capacity Report: Better Than Expected, and he reported a 0.8kWh degradation over the rated 18.8kWh or 4%. A Google search on i3 battery failures shows several hits on the 12V accessory battery (not even sure there is such a thing in the i4/iX), but no complaints on the high-voltage battery degradation or fire (Chevy Bolt, the EV owner's nightmare). For reference, Tesla's numbers (
Check Out This Official Tesla Model S/X Battery Capacity Degradation Chart) show an average of 5% after 25,000 miles, 10% after 100-150,000 miles and 15% after 150-200,000 miles, so the i3 owner above could be lucky or BMW's technology might be a bit better for long term reliability, though I would not draw a conclusion based on one sample. I'm eagerly awaiting the release of BMW''s user manual, to see whether they recommend the same "charge only to 82% daily, reserve the 100% to the road trip days to maximize the longevity of your battery pack" recommendation that Tesla provides.
Please share your thoughts! What's your confidence level that BMW will do at least as good as Tesla or even better in the long run?
