here's some advice from the experts at "batterycare.net" Read the full article here: http://batterycare.net/en/guide.html
Should I remove the battery when A/C is plugged in?
Many laptop users have this question and we will answer it right now:
The answer is: YES and NO, it depends on the situation.
Having a battery fully charged and the laptop plugged in is not harmful, because as soon as the charge level reaches 100% the battery stops receiving charging energy and this energy is bypassed directly to the power supply system of the laptop.
However there's a disadvantage in keeping the battery in its socket when the laptop is plugged in, but only if it's currently suffering from excessive heating caused by the laptop hardware.
- In a normal usage, if the laptop doesn't get too hot (CPU and Hard Disk around 40ºC to 50ºC) the battery should remain in the laptop socket;
- In an intensive usage which leads to a large amount of heat produced (i.e. Games, temperatures above 60ºC) the battery should be removed from the socket in order to prevent unwanted heating.
The heat, among the fact that it has 100% of charge, is the great enemy of the lithium battery and not the plug, as many might think so.
- Emphasis added
I have found all of the battery care tips at their website to be well-balanced and sound in theory and practice so far. I have a T61 which I keep plugged in most of the time. I bought it about a year ago. It came with a Genuine Lenovo Panasonic 9-cell battery which now has about 270 cycles and full charge capacity of about 75 wh out of 84 wh design capacity. Full charge capacity has remained virtually unchanged in about a year (I think it was at 78 wh when purchased last year with cycles around 200). It performs well on rare occasions that I unplug and use it on battery, and remains in "Good" condition according to Lenovo Power Manager. I don't think leaving it in a laptop which is constantly plugged in has diminished battery life in any way. Notice
: One thing I do if I realize I have not unplugged my laptop for over a month is to unplug it on purpose and let the battery run down to about 4% before plugging it back in. That gives the battery a work-out and keeps it well-calibrated. The remaining time calculated by Lenovo Power Manager as well as Windows 7 remains very accurate (If it says I have 30 minutes left, it really is 30 minutes left- no sudden shutdowns). Also notice this is a Panasonic we're talking about. Sanyo cells or Sony cells
will not perform as well in the long run, and probably require more pampering including more frequent "work-outs" and calibrations. They may also not endure "heat stress" as well as a Panasonic battery. My laptop does
run a little hot sometimes since I haven't had time yet to change a noisy fan which developed a few months back and since I overwork the poor thing. I usually leave it running night and day and just allow it to sleep when not in use. I do some video and sound editing, a lot of web-browsing/researching (with 17 windows constantly open), word processing (since I am a prolific writer), and a bit of video and music playing, but I don't do any "gaming." Actually, I don't think a grown man who is educated and has a life should be gaming on his laptop anyway LOL.