Quote:
Originally Posted by uboot
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Sorry but this is just one person's view and not definitive proof that using a wall charger has any significant affect on battery life.
I use both a USB port and a wall charger to charge my 650 and I can honestly say that I notice no difference in how long the charge lasts for. The only difference is that it takes longer for the red light to go out when using the USB method. One thing you must do is leave your reader charging after the light goes out as this does not indicate that the device is fully charged.
As I said charging via USB is perfectly OK - if it were not then Sony would be obliged to include a charger with every reader they sold.
You also must realise that the current drawn by the reader varies throughout the charging cycle. The closer the battery gets to a full charge the lower the current flowing. Theoretically when the battery is fully charged the current will fall to zero, but this almost never happens and the slope of the current curve will just flatten off. So if you charge your reader on a regular basis before it gets too low, as is recommended for long life, the potential difference between the 5v USB source and the battery voltage will be such that it's unlikely that you would exceed the 500ma available. There also must be some circuitry in the reader that limits the charging current as charging the battery at too high a current will destroy the cells.
So to sum up. In my opinion there is no reason why charging using USB is any worse than a separate wall charger. As long as you do not let your computer go to sleep and you also leave your reader connected for long enough, then there can be no difference.
After all at the end of the day it is just down to the laws of physics!