> Amazes me they don't just sell it like that everywhere because it sounds a lot like a product improvement...

I'm not so sure. The first laptop I bought, a Titanium Powerbook, had replaceable batteries. And even better than that: you could hot-swap them while the laptop was running on battery power, and the laptop wouldn't even shut off. It felt leagues ahead of even modern replaceable battery functionality, and honestly? After owning that laptop for years, I felt like I just wasted my money with that additional battery.

Part of it, I'm sure, was that I didn't have an external charger to charge the battery not currently in the laptop. But on the whole, it just didn't feel like it was actually worthwhile, and when Apple stopped shipping replaceable batteries, I've never missed it.

(Hot swapping the batteries really was awesome, though)