Battery replacement:
In 2020 I elected to replace the battery as I would often find the battery flat when I came to use it. Replacing the battery was pretty straightforward thanks to a guide on Youtube. The only thing to note is the various screw sizes and the plastic strip surrounding the body is easy to break; mine turned out to already have a crack in but it all went back together ok, held together with the double-sided tape already in place.

Quirks:
One quirk I sometimes had to contend with would be the Reader would freeze following a full charge, oh, and it could only be charged from the 5v power adapter rather than USB.

Update/review - March 2018:
I had some good use out of my  PRS-300. It's was handy for putting on those free books I find online, or even essays that are too long for me to read on my computer, and that I can't justify printing off. However, I do struggle with longer books on the device; generally because of maintaining attention which is also hindered by the action of turning pages which can be sluggish for some formats, particularly where formats have been converted.

Bookmarking pages, while possible, is not ideal because this only marks the page and not the particular point I want to highlight (typically I would leave a thumbnail indent in a physical page or a light mark with a pencil so I can refer back to it with relative ease). I find an eReader is better suited to the type of book or document that can be dipped in and out of, and particularly those that I'm not going to want to flick back and forth between pages or turn to appendices or indexes, because doing so with digital documents (not just on eReaders) just isn't a smooth way of working. If I can find a cheap copy of an actual book on Amazon then I would prefer to buy and read that instead.

I had a month of access to Amazon's free eBooks in 2017 I believe, and while I was able to download a multitude of titles (and then converting them to .epub without the DRM in place (which also required a month's free trial!)), I only got round to reading one short one, illustrating that "all you can eat" isn't always beneficial.

I eventually sold the PRS-300 after acquiring a PRS-600.