Many PowerBook/iBook owners use two batteries on a regular basis, especially on long airplane trips. But once you get to your destination, you've got two dead batteries. If you use your laptop to recharge them, you're in for a time-consuming experience. If your laptop is an iBook, this'll take even longer, as you'll need to shut down the computer to swap batteries.
Consider using Newer Technology's external charger/conditioner. It can recharge two batteries at once, and recondition them as needed.
Due to the fact that Apple uses slightly different batteries for most of their laptops, Newer makes several different charger/conditioner models. The Weeks Division of MyMac.com Labs tried the model for the 15" Aluminum PowerBook. Links to Newer's other models can be found here.
The unit is solidly built, so much so that it may be cumbersome to travel with. There's a substantial external power brick, as well as a conveniently long power cord. The manual is a small printed sheet that explains the meaning of the colored status lights on the front panel. Most users will glance at the manual once, and then never need it again.
Charging a battery is a simple matter of dropping the battery in the right slot, and waiting until the status L.E.D changes from flashing green to steady green.
Conditioning batteries is just as easy; drop the battery in the left slot (the left is the only slot that can condition), and press the conditioning button. The unit will completely discharge the battery, and then fully charge it.
While the LI-Ion (lithium ion) batteries used in all current Apple laptops are less prone to the "memory effect" than older NiCad batteries, Newer states that even LI-Ion batteries will benefit from periodic conditioning (discharge/charge cycling). In non-scientific testing, I found that my original AluBook battery picked up about 15-20 minutes of endurance after 4 conditioning cycles over a week of use.
One unfortunate side effect of Apple using different battery form factors for various laptop models is that you have to purchase a charger for your specific computer. If you get a different iBook or PowerBook, your old charger won't work.
If you own more than one battery for your laptop, Newer's charger/conditioner is an easy to use, solidly built unit. The main disadvantage for road warriors is its bulk; the charger is too big for most laptop bags. For home use, size is not an issue.
The unit works well as a charger, and periodic reconditioning will help get maximum life out of each charge.