For me, I use the WakaWaka Power+ in the emergency kits I keep in each car, along with a spare set of cables. Each is good for one full charge of an iPhone 6, has extremely low self-discharge, and recharges itself in almost any amount of sunlight. I also use these when camping.

For shorter excursions I use a non-solar LiPo powerpack. I don't have the model you look at but those have a lot of claimed capacity for the price.

It's essential to top any devices like this off every month or three (depending on how much it self-discharges) and every time you use them if you want them to work when you need them.