So I was seduced by this battery fitted with a solar panel: no need to charge before going, you can hang it on your bag or elsewhere depending on the position of the sun, and it charges itself: -) Small detail practice: A green LED confirms that the panel receives enough light to charge the battery.
With a capacity of 6000 mA / h, this battery can simultaneously charge two high-end smartphones with its two USB outputs. However, planning to load the night: the exit 1A is a little less powerful than your regular charger.
For gray winter days, know that it is possible to recharge the battery from any USB charger or computer USB port.
Finally, since it is intended for outdoor use, this battery is waterproof to water spray (rain OK, but do not soak), and is surrounded by a shockproof rubber band. The build quality is good
The current price, thirty euros, is very correct for this battery that can be recharged even in nature.
Erwann on Amazon.com