You're definitely not the only one - it's just that this is more of a personal choice than a trend. I get why your friends laugh - honestly, for most people a phone has become a universal tool. But that doesn't mean printed guidebooks are outdated. People just travel in different ways. Some rely entirely on Google Maps and reviews on the go, some mix approaches, and some prefer the book version specifically. That's totally normal.
A guidebook really does have things that apps don't. You can prep at home without stress, highlight what interests you, notice details that an algorithm won't suggest. Flipping through it with a cup of coffee at your hotel - that's a pleasure all on its own. And most importantly, like you said, you're not dependent on a battery. If your phone dies, you still know where to go and what to see, you don't panic. I think it's a sensible approach, especially if you're going somewhere with spotty internet.
Plus handwritten notes actually stick with you - you'll remember the route better than if you just scroll through a map. It's like knitting: you can watch tutorials on YouTube, but plenty of people prefer a printed pattern on the table. To each their own. Don't listen to the teasing - go with what works for you.