That might not always be practical; taking out the battery means having to turn off the device. That, in turn, means you'd have to interrupt whatever you were doing
Using the solar panel might not be effective in the winter, however, on the beach where i stay all day due to my condition to benefit from the air, if kept at 90 degrees from the sun will pretty much remain charged all day. Sure, wont charge the laptop but it is enough for a regular android phone to browse and listen radio over internet.
As I said, my small minizi device is making sure I have power in my phone all day even though I listen radio and use GPS navigation. I made a mistake, it is 5600 mAh, not 5200 and my phone is a quad-core full HD (1920/1080) 5", eating through the battery on dual standby and only wifi on in 2 days. If I add GPS is eats it in 1 day and listening to radio over 3G in places with low signal makes it go down in just a few hours, no to mention running RDP with bluetooth mouse and keyboard.
The minizi is small and compact is not weighting more than the phone. Is it practical ? Could be a lifesaver if you get stuck someplace in bad weather and need to communicate, for 8 USD is definitely worth it also.