Solar is a great alternative.
The Renogy 10w solar panel is a portable solar module. It is from Renogy and they call it the Renogy Portable E. Flex Monocrystalline 10 Watt plus Solar Panel.
It comes with a 5V/1.9Amp USB port to charge and maintain a
variety of USB devices.
Also, two carabineers which help you to attach your panel to a backpack while hiking. As well as 4 suction cups for easy mounting in vehicle windows for easy charging.
The solar module comes with 2 X 5watt panels and a charge controller and cable.
The charge controller comes with overcharge protection.
Also smart auto-optimization charging. Auto-optimization technology detects when charging drops due to changes in light conditions. This can be due to shadows cast by trees, clouds, or other objects.
To prevent underperformance auto-optimization charging prevents undercharging due to these reduced levels.
When light improves charging will immediately return from the reduced level.
This is a vast improvement on delays in charging times of USB devices.
Maximum Power: 10W.
USB Charging Port: 5V/1.92A.
Operating Temperature: -4°F to 158°F.
Monocrystalline Cell Type: 22% efficiency.
Folded Dimensions: 0.3 x 6.3 x 0.16 in.
Unfolded Dimensions: 13.4 x 10.3 x 0.08 in.
Weight: 11.2 oz.
Solar Panel Surface Material: ETFE Laminated.
Fabric Material: Oxford.
Operating Temperature: -20°C to 70°C.
Other on-the-go activities;
Hang it via carabineers;
Put in window with Suction cups;
Pair this product with a power bank for more user satisfaction;
(A Renogy Drifter portable battery bank works well for storage of back-up power.)
To charge a USB device you unfold the solar module and direct it to the sun. Plug the device into the USB 5V/1.9 Ampere port and it will be charging.
One can also do stored charging. Connect a USB powered battery and you will have stored power for longer periods.
For added flexibility you can hang it to your backpack by making use of the carabineers.
Also make it a window charger by using the suction cups to use it inside a vehicle or at home.
When raining, water can enter the USB port. A type of rubberized flip down cover could prevent water from entering.
When you mount it on a back pack you reduce performance.
This is due to movement and thus poor positioning. Remember though that by doing so, you add much more charging time while hiking.
The 10 watt E-flex is not water proof, but it is water resistant. Take care of the USB port. Water and dust could cause damage.
It is for USB charging at 5V/1.92A max.
The Renogy 10w solar panel comes with a ruggedized surface. It will not scratch, shatter or damage.
This is a good lightweight solar module and it takes very little space in your pack.
The Renogy 10w solar panel comes with a 1-year material and workmanship warranty.
Renogy is a top level maker of solar panels. They Renogy 10w solar panel very well and it comes at a good price.
This is exceptional value for money and can be a good long term investment when buying.