It all depends on your reading habits.
If you ask me, the PW has a too low battery life.
Lithium batteries last longest when always having them charged, but never over charged, and NEVER fully empty them.
They could enter into a state of no return if they get depleted too much (read up on the internet about this phenomena).
Generally I don't like to charge my battery to 100%, neither deplete it below 50%.
If your PW lasts 10-12 hours on one charge, and you are in the habit of reading 8 hours, then charge it in your breaks, keep it plugged in while reading, or charge it after you finish reading. 60% is just an indicator. I've been working with Li batteries since the 1990's, and have found they usually last for 2+ years, when charging the battery above 50% of their charge.
People who are in the habit of emptying the battery completely, or waiting until there's 10% left in them, usually experience a 20+% decrease in battery life after the first year, and have to throw away the device after 1,5 to 2 years (depending on how much they use it).
On my devices, usually after 2 years, I would have 80% left of charge, and after 3-4 years, I'd have to replace the device.
This is going to be the problem with current devices. Though the quality of Li batteries has been improved significantly in the past years (We're no longer in the 1990's), and current technologies may have extended battery life, I still see 4 years down the road, all of our devices need to be thrown away, Amazon charging double shipping, and a $25 fee for replacing those batteries,...
My Sony PRS-505 hasn't been used in ages, and has reached multiple times zero charge, is from 2008, and has 10% of original battery life left.