If you studied the ROI for dollars and time spent on this sort of thing, I believe if you showed it to the Shark-Tank folks on TV, they would show you the door. Every solution has a problem, but for most laptop users, Josephur's solution would be way over the top. They don't even like carrying around a mouse-dongle for an external mouse let alone a small circuit board and a 2nd AC adapter in there.
And, for many laptop users who are forgetful, they forget their AC adapter (the one that powers the laptop), their external mouse, USB flash drive backup, etc. when they show up to a place outside of their home with their laptop.
This happens all the time with students in my Classes, and just yesterday as a matter of fact, one lady in my Class knew she was coming to a class where she needed her laptop and all her accessories, but could not remember to bring her mouse since she couldn't use the built-in trackpad.
What if she had this external circuit board and a 2nd AC adapter to carry around too, think she would have remembered to bring that also?
It's an ingenious solution to a tricky problem, but how many people of a billion laptop users would actually use something like this to save $15-$35 for a new replacement laptop battery? Not many, is my guess.
Buying a laptop without a self-servicing type battery, is just asking for trouble IMO. Especially when it's been well established here and elsewhere that 95% of batteries from the major laptop makers fail within 1-2 years, and even less if they are installed in Gaming laptops such as Alienware-Dells or MSI.
This is like many new Cell phones which did away with the ability to open the case and remove the battery--this is stupid IMO and I would never buy a phone without that capability. I just had to make that decision last December when I bought my latest Cell phone.
BBJ