Among the great variety of things that we can take on our adventure trips or outdoor activities in general, battery chargers are among the most functional; today it is possible to purchase solar battery chargers of all sizes and for all purposes.
In the context of urban survival or travelling for a long time with some sort of vehicle, if you carry telecommunication devices, cell phones, radio transmitters, scientific instruments, etc. you should have some way to reload your batteries; backups may not necessarily be enough.
Frank Wolff filming as Gustavo Sakuda lits a fire in the wilderness; a lot of batteries are usually needed for these jobs.
There are a lot of choices now, so there is no excuse. You can even purchase the individual solar panels that you can use to make your own specially-designed solar chargers, or combine these with wind or hydraulic generators in order to produce a lot of energy under all circumstances.
In the context of wilderness survival situations, a solar battery charger may prove inestimable. If you are far away from an electricity source, it is likely that you will depend on the batteries you carry with you during your excursion or have during the emergency situation.
A solar charger in action.
And while you can survive without any sort of electrical energy source - of course -, things may be easier if you have something like a torchlight or a GPS at hand, and even more mundane things like camcorders or digital cameras. Your reloadable batteries will turn you into a more independent, self-sufficient adventurer or survivor: even in a city we can experience serious emergencies like widespread blackouts, terrorist attacks, floods and earthquakes that may devastate the electrical grid. So, solar chargers are useful even within the context of urban survival.
Another key issue is that to reload environmentally-friendly batteries using a solar charger means that you will be contributing to conserve our world and avoiding to contaminate it more than necessary: rechargeable batteries last a thousand times more than traditional ones, so if we all would use them, we would improve our standards enormously in that department alone.
Cameras of this kind don't admit second-rate battery loads.