Quote:
Originally Posted by rleguillow
With these devices, does it hurt the battery to leave it plugged in when not reading it? So far the usual I've done is overnight, so I haven't a clue. I recall being told if batteries weren't fully discharged that they sort of forgot their real capacity... but I don't know what kind of batteries those were (if it was true at all).
I learn so much from these forums - I'm sure I'll get an answer for this one. 
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Leaving the device plugged in will keep the battery topped off at 80% to 100% charge.
According to Wikipedia a lithium battery that is fully charged to 100% can loose a little capacity every year, but in practical terms it depends on where the Sony engineers set the upper charge termination point.
Sometimes for longer cell life in devices without replaceable batteries they set the upper charge limit a little lower than the actual 100% point to avoid the peak charge effect reducing the capacity over time, and if this is the case you can basically leave the device on the charger forever with no ill effects.
I had a cell phone that I left on constant charge every single day when not in use for several years on the same lithium battery, and at the end of that time the battery had lost only about half it's original talk time.
One thing you do want to avoid is letting the cells drop all the way down to fully discharged, which is many times more damaging and can destroy them quickly. The Sony will shut down before this point is reached, but if it is then not charged for several weeks, the small residual drain in the circuits can flatline your battery and kill it.
So by keeping it on charge, you could loose a little capacity over time, but very little, and it's better than the alternative of letting it go dead, because if that happens, particularly to an older battery, it may just die and never hold a charge again.