I am currently using a recently acquired VAIO as a home computer whilst my old tower which died is replaced. It is hooked up to the mains and I have been letting it run down, then recharge and so-forth. Is this good for battery life or shall I just leave it plugged in and fully charged all the time?

I'm pretty sure both are "bad". I seem to recall that with a lithium-ion battery ideally, you discharge it to 40-50% every time and then charge to full. However, of the two (frankly, more sensible) alternatives you've listed, charging constantly is "least bad". Lithium ion batteries don't like being discharged too often.

I have a VAIO GRT996ZP that has spent most of it's 5+ years on the adapter. On the occasions where I have used it on battery, I haven't had any problems.

Right will leave mine on all the time then. Still going to unplug the adaptor when its turned off though as no point having that thing on when the laptop is shut down & fully charged.

If you are using it on the mains, just remove the battery.

If you are using it on the mains, just remove the battery.

There is a warning on most VAIOs telling you not to this. Some won't start up and just flash the power and battery lights alternatively. In the case of a power cut you will kick yourself when you lose what you are working on

Right will leave mine on all the time then. Still going to unplug the adaptor when its turned off though as no point having that thing on when the laptop is shut down & fully charged.

That will also kill the battery. Batteries have to be used or they die. Your first idea is the best, leave it on mains but let it run on the battery once a week so it gets a discharge cycle.

According to Apple when talking about an iBook..

You need to let it run from full to empty (in the ibooks case it forces it to sleep).. once a month or so as it "conditions" the battery monitor / circuitry to give decent readings about how much powers in the battery..

However, they also say that 1 full cycle ISN'T strictly from full to empty, but that charging it from 90% to 100% 10 times still only counts as one cycle? If ya catch my drift?

Personally, I've seen more batteries killed by being left attached to desk bound, always plugged in lap tops then I've ever seen killed through full cycling. I have a laptop from 1999, it's lithium, I always fully charge and then fully drain it... it still gives 2 hours use.

Thing is, the circuitry's quite clever in them now and if you're only using it for a short while I don't think it'll make much difference how you treat it, maybe just let it run from full to empty once or twice.