> On Apr 9, 2026, at 5:44 PM, Joel Phelps <
joel.e...@gmail.com> wrote:
>
> I’ve seen the BYD batteries mentioned in the British motoring press. It sounded like the blade batteries were a way of building the batteries in a format that was more efficient for the anode shape and also for thermal management. For a long time, just about everything from flashlights and power tools used the 18650 battery format. It was at least 6 years ago, but I remember a Tesla car being referenced as having thousands of these 18mm diameter by 650mm long batteries. This seemed to by very typical for EVs and it was unusual when the Nissan leaf had custom sized flat batteries. I also remember references to prismatic batteries which were supposed to have less wasted space. BYD is a huge company and they are a battery producer. They sell a raft of models of electric cars in Europe.
I think Boeing did the same when they created Li batteries for the 787, and had trouble. Yes, prismatic batteries would seem to save space, but it's not so clear given that car propulsion batteries need a cooling system. Cylindrical cells can be stacked pretty closely, and the space left over can carry cooling pipes.
Quite likely the 18650 was picked by Tesla because it was a standard type, so they could just order a suitable number of millions of them and not have to deal with yet another problem, the creation of a whole new manufacturing line just for the batteries. BTW, I'm pretty sure they are 65 mm long, not 650. From pictures I have seen the Tesla battery packs have the batteries nicely arranged standing up vertically, in a number of compartments constructed to act as fire blocks. The resulting pack is also a structural element.
paul