I think you're completely missing the point mate! If I have a 96kg luggage allowance + an arbitrary 7kg hand luggage allowance (which is quite typical on my tickets, 64kg standard plus 32kg extra as my OWE allowance) why do you care how I distribute it? You're not paying for that, I am and it's my entitlement for earning that level of OW status. I typically only use around 20kg of my check in allowance. A bit of extra weight in my backpack from lithium battery devices means nothing in the big picture. I'm not the one trying to maximize every gram I can between checked luggage and hand luggage nor skirt checked luggage charges because I fly business and am OWE so that's very generous already, I just can't check in certain stuff due to international regulations.

And BTW, why don't you check into how much of a PITA it is to ship lithium batteries by air as a non-commercial shipper... let alone customs issues since it's not arriving together with you. You're clearly very short sighted on all of this, and very glad you can live with a MacBook Air.