After returning from holidays with completely drained PRS 500 (see field test blog entry), I have decided to test what is the battery life of the fully charged reader without any usage at all. It was easy as I was pretty busy after being away 3 weeks.
The reader was fully charged on 29th of August (24 hrs with wall charger). After that, I did not use it at all, only checked every 2-3 days the status (the reader was switched off except this brief check). As of Wednesday morning, September 19th the battery was drained and the reader switched itself off right away (it is being charged as I type this). This gives us about 3 weeks of available standby time, without any use from page turning, until the fully charged battery is completely drained.
This result allows new angle in looking into the "7500 pageturns story". Let's assume that the battery indeed lasts for 7500 turns and let's factor in the consumption of standby. When the reader is off, every week will take away about one third of the charge - or in other words you will loose battery capacity equivalent to 2500 page turns a week regardless whether you switch it on or not.
If you would turn page every 2 secs, 30 pages a minute, 1800 pages an hour, chances are that you might get closer to the ideal capacity. But if you read a book with a speed of 200 pages per hour (these are small pages) and have have time to read 2 hours a day, during you will "spend" about 7 x 2 x 200 = 2800 page turns - plus the weekly standby tax of 2500 page turns. With this, you will have available about 2200 turns - or less than a week in standby and if you will continue to read, you will have to recharge in about 9-10 days. Which is quite consistent with what I have seen o vacation: the reader died after two and half week (~ 6000 turns) plus about 1500 real pages.
So, the 7500 turns may not be such an impossible number - if you can read 1000+ pages an hour :-).
With the size of the screen, depending on the font and real page count books are anywhere between 500 and 1500 turns long. That means, one full charge is realistically good for 3-4 books.