Additional laptop battery instead of DVD-rom'a?

Question

Batteries

I saw excellent examples of laptops in which instead of DVD-rom'a you can put an additional battery.
I understand that this only applies to specific laptop models, right?
Has anyone come across instructions for creating such a battery and the corresponding alteration of the laptop?
(Examples: www.portcom.ru/articles/196 , belkashop.com.ua/index.php?news=yes&npost=219 )

Answer 1

Yes, it applies to specific models.
There are no such instructions - a laptop lithium battery is not just batteries, just like the laptop power system itself is not just wires.
It is possible to do that, but it will be a Frankenstein with dubious benefits.