Originally Posted by T Stew

That is sort of the route I am heading. I like using my phone since it is pretty versatile, I already have it, and I like looking at the gps maps and stats and all. The battery is a bit on the small side now-a-days at 2000mAh. The phone I bought my son has a 4000mAh battery. So battery life is greatly dependent an what particular phone you have. Some are even less than 2000mAh.

I did a 3 day trip last week, first and second day 82-83 miles each. First day I had my phone on like normal, tracked with GPS and endomondo, plus I did have to use data and google maps to figure out some hard to follow trails for a bit. My low battery (15%) warning kicked on when I was still 15 miles from my destination. That night I was able to plug in. Second day, same distance, I tried to see how I could improve battery usage. I did a fresh reboot to insure I didn't have a bunch of background apps using any extra power. I went right into airplane mode first thing in the morning, and I downloaded some maps to a jpg file ahead of time so I could just look at a picture instead of turning data on and google maps. At the end of the day I pulled into the campsite, and setup my tent. Did a screenshot after I unpacked in the tent, 6:48 PM, was at 59%.

Technically I could have shut the phone off overnight, and made it through another day on the same battery charge. But I brought along an extra battery plus a portable usb power pack - one that uses replaceable 18650 li-ion cells (I have several 3400mAh cells for flashlights). So I plugged it in overnight and charged it back to full.

I figure with just the extra phone battery I could have gone 4 days, with gps and Endo running around 8 hours or so each day. And then of course with a portable power cell I could get about 2 more charges (4 more days?) for each li-ion cell I brought along. Seems like even with some phone usage in there, a week without power wouldn't be an issue, especially if you could use airplane mode most of the day. That might be unrealistic for some folks with families though, or those who need to stay reachable for work or something. My son was on an Alaskan trip at the time and I was not expecting any phone calls. I didn't even have phone signal for part of the trip anyhow.