I'm about to leave on my first multiday trip on Monday.

I will be traveling on mostly hiking trails and have made a GPX file for me entire route (around 400km). For my previous day trips or overnighters i have followed the route using the app "Ride with GPS".

What i am concerned about on this longer trip is battery life. I also use my phone as a camera and posts to instagram along the trip. That can be very battery consuming.

I have 2 power packs with me, one with 4500mAh and a larger one giving me 20000mAH

The trip will take something around 5 days and I am looking for some advice how to limit battery usage and still be using the phone as a tracker/navigator.

You may know this already but putting your phone on airplane mode doesn't typically disable the GPS function. You can turn off airplane mode for Instagram uploads. I've found that airplane mode saves significant battery life.

What phone? If it's an iPhone, you can use low power mode. Android also has a battery saver mode, but I think it disables GPS. In either case, you can do a lot of the things that these modes do by themselves--turn off bluetooth, turn down screen brightness, turn off anything that is fetching data. Of course, if you have the screen running with your GPS app on it the whole time, that's going to dominate your battery usage, so the best thing you can do aside from turning down brightness is to try to turn the screen off if you don't need to look at the app for long stretches.

Also, if you can tell the app to space out GPS location fetches, do that.

If you're in an area with sketchy cell coverage, the phone utilizes significantly more power constantly searching for network connections. We ran into this in western, lower Michigan and the U.P.

It you have periods where you don't need the phone, just power it down. Restarting, my Samsung 6 is pretty quick.

Airplane mode remedies that

if you map out your route first you may not need the phone too often. when we tour my gf's phone is the backup map for when we lose our way, which does happen fairly often. for emergency contact with the outside world i have a flipphone that stays charged for a very long time.

I've used a separate point-and-shoot camera and a USB cable adapter to connect to the phone to send the (few) pictures that I wanted to share immediately. The camera was very compact and I have enough of an interest in photography that it was worth it for me, but of course, it is another gadget to carry.

Your battery capacity seems to me like it would be enough. I've done three days with 2000 mAh in the phone and 4400 mAh in an external battery, and it was plenty. Very little photo-taking with the phone, though, but GPS tracking running and some podcast listening at night.