I go back and forth a lot when it comes to buying books. Having spent so many years in college, I amassed a large quantity that I have stored away. Prepper books are no different. I purchased a lot of physical books over the last year, but I also bought some e-books, as well. I didn't own an eReader at the time, but you can download a Kindle app for reading on your computer so I did. I did save a few on my Droid phone, too.
For Christmas, the wife bought me a Kindle Touch. I love it! I have probably downloaded 20 books since Christmas. Many of the e-books are cheaper than regular books and I get them immediately. I can flip through them, highlight and recommend them to people through social media. I have downloaded books about DIY solar arrays, weapons, homesteading skills and many others.
The questions is: Should I buy e-books or physical books? So let's look at the pros and cons of it.
The Pros:The Kindle allows you to save literally thousands of books and other media in one small, flat, lite, compact source. Physical books are tough and barter able.
The Cons: The Kindle is an electronic device, not water proof and must be recharged. Books are heavy and take up a lot of space.
So what do we do? I say, buy both! Some books are just too good to have only on Kindle. For instance, The Encyclopedia of Country Living. You should have this book in Kindle AND Physical editions. I tend to look at books on Kindle, and if I deem them absolutely necessary I buy the physical versions, too.
If you have a eReader, you should have something like this. It allows you to charge an external physical battery that you can plug you eReader into to charge it. It will also charge other USB devices. I don't recommend a specific solar charger, so do your due diligence before you purchase one (or more).
A note on EMP's. An electromagnetic Pulse MAY make your eReader unusable. This is why you should have both digital and physical copies of those "can't live without" books. However, it should be noted that experts disagree on the extent of the damage an EMP will do. If you want a worse case scenario read on EMP, check this book out. One thing is for sure, an EMP will knock out power grids all over the US at a minimum. So the solar charger is not a bad idea anyway.