As a quick answer, no it is not a good idea to have it used like that. Rechargable batteries enjoy being discharged, and then recharged again. They may take 200-700 charges and still be happy then :)
After you buy your new laptop, it 'should' be charged fully, then used on the laptop on its own (charger disconnected). Do that until the laptop switches off due to no power, or Windows/Linux says the power is below 10%.
If possible, do this 3 times, then your battery will have 'learnt' its full potential, and will be ready to give good service life.
It will still work ok for you as you are doing now, but it will most definatly have reduced its working life.
**and here's a longer explanation** ;-)
Laptop batteries come in 3 general types, named...
Ni-Cad (a very old design, not used since about 1999)
Lithium-Ion (the standard for all normal batteries now)
Lithium Polymer (the latest thing) :)
Ni-Cad types are only short life things, and if you get 12 months use from it you are lucky. It is 'essential' with that type they are fully charged, then completely discharged, and you have to keep doing that...if you don't, they start to hold less and less charge over time (this is usually called memory-effect). But these go bad quickly anyway (note that this is not guaranteed though - i do have 3 Ni-Cads from 10 years ago that have survived in old laptops)
Lithium-Ion is the most common type, and when these were first introduced, the manfacturers claimed the 'residual memory effect' had been removed....but, well, it hadn't really, it just wasn't as bad as with Ni-Cads. These batteries are very very good, but they still like to be discharged about 1 in 5 charges, to keep them healthy.
Lithium-Polymer is the top of the range for now, and these have 98% no memory effect :) They can last longer off a single charge, they don't fade with non-use, and are generally all-round good things :) But, they are usually very expensive too :(
If you have issues with not enough battery life, consider buying a new lithium Ion type, and charge as said earlier...also consider getting maybe TWO batteries if your laptop supports that feature. A COMPAQ E500 can take 2 batteries, and gives over 8 hours of mild use. Many laptops can have a floppy or CD drive removed and the 2nd battery fits in there.
Remember that rechargables (all of them, not just for computers) love to be drained by high power devices. Its the main way to keep them healthy.
Final note - some older laptops have an issue called 'over-charging'. This means the charger just keeps pumping power into the poor battery even when it's fully charged already. This idea should not a problem on modern laptops, but I would still not recommend leaving anything plugged in constantly.
Hope that helps somebody :)
Philbert, November 2007
