Anker batteries come in a zillion sizes, are cheap and are safe to plug into public chargers. With how hungry phones are these days, I don't know how people live without portable batteries.
Back when I used android, it was much more common that runaway apps would drain my phone in 2 hours. But now? Doing a anker battery would be lugging around a bunch of dead weight.
Basically, the phone’s battery life depends on disabling hardware components, or running them in a low power mode, as much as possible.
Modern GPS chips only need around 25mW apparently - older chips can pull 100mW though. Scanning needs a bit more power than tracking.
On phones I think the problem mainly is that the GPS needs to wake up an app that need to handle the GPS data and then do some calculations. You can easily get data ten times a second that is alot of wake up from sleep, and probably draws lots of CPU.
I think most of the drain comes from that rather than the GPS unit itself. But people might say "using my phone's GPS uses a lot of battery."