I believe the 3 main options for portable GPS currently are:
They all have somethings in common, and each have other considerations also. For this question, if my only concerns are GPS and battery life. Out of the box and/or with available modifications, what are my best options for battery life per dollar?
Related: What are some ways/devices that I can use to charge my batteries in the wilderness?
From your three options, a Dedicated GPS unit is going to be your best bet.
Smart Phones barely last a day. If you're out of coverage, the phone will keep searching for network and battery will die as quick as a cat fight. Of course you can use the airplane mode but we all know how long they last.
GPS watches do last a long time. It will vary a bit from brand/model to brand/model. I picked randomly 4 Garmin ones and I got from
So you could make usage of a full on all features on for to long.
A dedicated GPS unit / handheld device picking 4 randomly similar low, mid and top range, all work on AA batteries and last for 25 hours (besides the top range that comes with a removable, rechargeable lithium-ion battery pack and last for 14 hours.) But even lasting less than the watches you can easily carry another few batteries. Lasting 25 hours, you could easily have it on for a your whole walk (8 hour / day) for 3 days.
I believe the trend is to build a device to suit a specific need. The watches are good for short trips running while GPS devices are more long trips.
As a side note. I bought one of those portable solar panels (Go Zero, I don't remember the model) to try to recharge things. I think it was a waste of money. On a long hunting trip (a week) I tried to use it and it was cloudy most of the days. I tried to charge a couple of batteries without success.
IMO as biggest and greatest the techs are nowadays I would only trust on batteries for my head-torches and electronic devices :)
the airplane mode but we all know how long they last. about 14 days, here. But that means not using it as a GPS, too.
Stretch target: 10 days of GPS between charging points with minimal additional weight
I'm planning some long on-trail thru-hikes where digital mapping would be much lighter and more practical. But I'll be up to 10 days between charging points in climates where I can't rely on sun. Can this be done?
This is doable for navigation using a phone or a dedicated GPS
Given the many advantages of smartphones over a dedicated GPS, a lot of people have been researching the ins and outs of keeping them going on the trail.
The best source I've found is this comprehensive article by Alan Dixon, the co-founder of Backpacking Light and an actual rocket scientist! Alan and his friends have established protocols that keep a modern phone operational for 5-10 days between charges. To achieve this, you'll be setting up the phone carefully to minimise drain and activating the GPS manually to take bearings as needed. A number of other bloggers confirm that this is doable.
This is similar to the battery life reported by GPS users who only take bearings on an as-needed basis.
For on-trail work I would plan to supplement this with route cards, and by printing out sections of maps for any particularly tricky sections or exit routes. On a trail, this should be fine.
As insurance, most people seem to carry a 6000mAh external battery. This should give you another couple of charges and can be topped up pretty quickly when you hit civilisation, especially if you use one of the fast-charging options. At least one well-known thru-hiker takes a second phone for additional safety, and this would give additional usage time if things go wrong.
For serious off-trail work I personally would be taking maps and using GPS mainly for confirming location. There are some shortcuts that simply aren't worth taking.
For tracking you'll need a dedicated device like an InReach
If you plan to be days between charging points, you can forget about tracking with your phone. Users report battery depletion at around 5% per hour. You're going to have to carry a huge external battery that takes many hours to recharge in every trail town. No-one seems to think that this is practical. Dedicated GPS won't last much longer.
But it should be doable with a dedicated tracker such as an InReach, which is optimised for precisely this requirement. It has a phone-sized battery that lasts up to 100 hours.
If you have the budget, a watch would be a useful supplement
At the time of writing, the top end Garmins and Suuntos claim 40-50 hours of battery life at the slowest update rates, and they only require around 300mAh to recharge. So keeping them going is practical with a small external battery.
Of course they won't give you mapping, so they aren't a stand-alone solution. But they would greatly reduce the need to fire up your big phone or GPS during the typical day. They offer a lightweight altimeter, and their ability to sound an alarm if you drift off route is very attractive. They would be part of my ideal solution.
Hope this is helpful!
A dedicated GPS is likely to have better signal as well as better battery life.
The key is that you don't have to run it all the time - if it's had a fix within the last few hours it will pick up in a couple of minutes. It's rare to need constant GPS especially with a paper map and a compass (which you should have anyway). So a fix every half hour or hour is often reasonable. Carry the GPS on the outside of your gear and you can turn it on in advance of a planned stop. Clipped to a shoulder strap works well.
Even my old etrex runs for 20-25 hours off a set of alkaline batteries (forget NiMH, they're too low voltage). Turned on for 10 minutes per hour that's over 100 hours off a single set of batteries, or 10 hours on each of 10 days. So with a single spare set of batteries you've got plenty of margin.
A phone is a good backup GPS especially if you've also downloaded maps. But I suggest that it's kept switched off with mobile data and WiFi disabled first (so they don't use battery while it's getting going)
