this is what i do ,when i can use it plugged in i do, when i cant plug it in i use the battery ,dosnt heat to0 do it this way ,when plugged in and the battery is fully charged it stops charging ,so no damage is done ,really
As with any battery, frequently charging and then discharging shall inevitable do some damage, the real question that needs to be looked at is how much damage.
A laptop battery is specifically designed to be charged and discharged frequently, they are known as "deep discharge cells", meaning they can be run till empty without any major damage being done. Furthermore, laptop batteries are NiMH (Nickel Metal Hybride) or Lithium Ion which is a lot better at holding a charge, and can survive better than traditional rechargable batteries such as lead acid (the sort found in cars, which should be trickle charged instead of being zapped till full like a laptop battery).
To simplify things, a laptop battery is fine to charge and discharge regularly, and it is fine to keep them plugged in even when full (just don't leave it unattended... blah, blah... usual safety warning). After a few years, you might notice that the charge isn't lasting as frequently, and at some point you shall want to replace it but until then there is nothing to worry about.
my wife left her laptop on for almost 1 month downloading a 80gig file from a very slow server ,no harm ,but i do agree that she really should not have done so!just foe safty reasons
It's a rare occurance for sure, however a friend of mine had a laptop which caught fire. I will admit it was due to a faulty charging socket and not the charging of the battery itself, but just as an insurance factor I thought it would be wise to mention it.
like any electronic device you need to drain the battery ( let it die) then keep device off and give a full recharge. As caperjack say if you have the facility to plug it in do so, but use the battery on a regular basis with out the electrical. only plug in when the PC say it need to be plugged in.
constant charging and not discharging will reduce the life of the battery.