A lot of us have been wondering how it was that Apple’s design team went off the rails when designing the new iPhone Smart Battery Case. Nilay Patel at The Verge, has now put forward one possible explanation: Apple had to find a way to avoid infringing the patents of the market leader in battery cases, Mophie …

Patel’s argument is that Mophie has a whole set of patents that cover the most obvious ways of designing a battery case that doesn’t suck. These include design patents describing the visual form. One patent, for example, covers a rounded back which – somewhat ironically – resembles that of the original iPhone.

Others describe various approaches to two-part cases.

The weakness in the argument is that there is no shortage of competitors out there with designs similar to Mophie. Patel argues these are too small for the company to pursue, while Apple’s exceedingly deep pockets would make it an obvious target. But those deep pockets also could buy the best legal team.

Mophie has an entire suite of patents on this kind of two-part design — here’s #8,971,039, which covers a slight variation of a two-piece design in which the top part slides over an extended piece of the bottom part. There’s also any number of design patents at play here; virtually every popular Mophie case has a design patent on its ornamental, nonfunctional elements. (For example, newer Mophie cases have a detachable bottom part; the company has design patents on that variation.)

One other factor that may have played into Apple’s decision. The one downside of Mophie’s approach is it makes the entire unit look extremely thick. Apple’s design does at least reveal that there’s a slim phone in there somewhere. When only a minority of customers will want a battery case at all, Apple may take the view that it’s more important what potential Android switchers think of the phone than the case.

Incidentally, Apple isn’t the only company to have opted for the “bulge” approach – HTC did something similar with the Droid Incredible 2 – and arguably made a worse job of it with the camera lens and flash within the bulge.