Convenient for who? Apple's explained, over and over, that a removable battery is a no-go in modern laptops, the amount of material required to encapsulate it and dock it eats up tremendous amounts of space.

Most people would rather have a 14 hour battery that's not replaceable than a 6 hour one that is.

I've had a lot of laptops in the last fifteen years and the only time I'd ever removed my battery was to add memory or a hard drive simply because it was in the way. Maybe one in a hundred people actually care about having a replaceable battery.