[User23]

Batteries used to have cardboard instead of metal shells. Because of this batteries used to leak prolifically. Then an inventor patented the modern metal shelled battery. His competitors all started infringing so he sued. They claimed that the invention was "obvious." The judge ruled that it clearly wasn't obvious, because if it had been they wouldn't have been making the obnoxiously stupid cardboard batteries for so many years.

[SoftTalker]

I'd still argue that it was obvious. They just didn't do it because cardboard was cheaper.