Why most magnetic power banks fail during long-haul travel (heat & speed)

I like the idea of magnetic power banks but they always disappoint me on the exact days I need them most.

On long travel days I’m using my phone constantly for maps, boarding passes, messages, and airport stuff. The moment I slap a magnetic bank on the back, everything gets warm. Then it feels like charging slows down and I’m basically carrying extra weight for a tiny trickle.

At this point, I end up going wired on trips because it’s predictable. I’ve been using an Iniu P63 when I’m traveling because it keeps up better than the magnetic setups I’ve tried.

Is this just normal for wireless charging when you’re actively using the phone, or are some magnetic power banks genuinely better at handling heat? If you travel a lot, what setup actually works for you?