My suggestion is yes. The battaries while lasting a good while if you pamper them 4-5 hours, really do detoriate. Getting two means they deteriate half as fast. So, its not the 8-9 hour charge you should want, its the 3-4 hour batteyr in a year which is the neccesity. For me my laptop which is a 1.5 Ghz PB with SD is almost never plugged in and if the battery deterioated into a 2 hour abtteyr in a year, it would render me useless as a couch potato.
I would love to see a way to charge the other battery though. I really woul dlike to have both batteries charge over night simultaneously, since I have two Power Adaptors.