As I understand it --- as in, what I've managed to retain from multi-hour conversations with IP lawyers trying to sell me services --- that's not actually how it works.

(a) if your broad claims and best-known-mode are insufficient to instruct someone as to how to build a battery, your patent won't matter, and

(b) just because you patent a 40-hour-battery concept doesn't mean you've patented the concept of a 40-hour battery. Every aspect of battery design that you didn't document and claim in your patent is itself patentable. You can patent technology that you yourself cannot build because of other overlapping patents.