Whilst I can't quite claim the length of use of pa42 (that must have been an Osbourne 1, "laptop" I think not!), my experience is that both types of batteries in common use on laptops (cheap Nickel Metal Hydride and better Lithium Ion) survive a limited number of recharges, and rather than use say 25% and then top them back up, they're better discharged down to 10% and then fully recharged.
Memory effect was limited to older Nickel CAdmium units as far as I know.
In the small print, I expect you'll find that the usual 1 year laptop warranty does not apply to the battery. My current Sony Vaio's first one lasted about 9 months.
Cheers - SLF