I need help picking a backpack to get as replacement.
I used to have TGS650 and the only issues with it were the elastic band breaking and the shoulder straps coming loose so I had to stitch a fold in the strap for it to be held in the locking plastic mechanism.
Requirements:
As waterproof as possible
Able to hold 15’’ laptop with power supply and 1-2 notebooks.
As comfortable as possible and not slipping from your shoulders even if you just are using one strap.
Bonus: has something to fasten elastic cords besides shoulder straps so that I can secure it on the scooter.
It will be used for hiking and going to uni but I only take one course or bring a laptop to the lab.
About 20 years ago I bought an Eddie Bauer backpack and used it almost daily. A few years ago it was really showing it’s age although it was still serviceable. I went to an Eddie Bauer store to buy another and told the clerk about my well worn EB that needed replacement. He said all EB backpacks have a lifetime warranty and bring my old one and he would replace it. I did and they did.
Are you dead set against another Targus? I bought a TXL-617 about ten years ago when I got a new 17" laptop at work and needed something I could put it in when riding my motorcycle to work. It’s got lots of storage space, and besides the shoulder straps there is a strap you can fasten around your waist, which keeps it nice and secure when riding the bike.
(Re-reading the OP - you want to fasten it to the scooter rather than wear it on your back?)
I’m not a camper so I can’t speak to how waterproof it is. But it’s spacious enough that I often use it as my carry-on bag when traveling. And it is very comfortable, even when I was lugging around that monstrous work laptop and accessories. (Although now my work laptop is a notebook that hardly weighs anything at all.)