Eventually batteries die, AC adapters give out, and hard drives go to hard drive heaven. If you think as a PowerPC owner your only options are eBay or other used parts outlets, you're happily wrong. I want to let you know about two online stores that specialize in new replacement parts and accessories for Macs including old PowerPCs.
Our first online outlet is MacWizards. They specialize in laptops and also have accessories for mobile devices. For everything from MacBooks all the way back to clamshell iBooks, you can purchase newly manufactured batteries and AC adapters made specifically for Macs. Their product pages are very helpful in determining which part is right for your particular model, and they also offer wireless antennas, MacBolt locks, car adapters, and more. They have a variety of shipping options and their prices are quite reasonable, so give their website a look.
Another outlet is Other World Computing (OWC). These people sell everything under the sun, including batteries and AC adapters for old 'Books, hard drives (ATA, SATA, and SSD), and also G4 CPU upgrades for your Power Mac. Their prices are similar to MacWizards, sometimes less, sometimes more depending on the part. And like MacWizards, everything's new and comes with a warranty. Just be careful browsing their website. It's easy to get lost in their huge selection and find your shopping cart suddenly full of hard drive adapters, iPod battery kits, and other accessories you didn't know you needed.
I was recently on the market for a Powerbook AC adapter and bought a Newer Tech model from OWC and had a good experience with them. It's good to know, with things like batteries and AC adapters, that you can still buy new and not have to cross your fingers on eBay.
Also, as another option, I want to point out Low End Mac's Amazon store for a wide variety of Macs and accessories (and purchasing through their Amazon storefront helps support Low End Mac). The fact that six years have passed since Apple abandoned PowerPC and there's still a market for these parts shows the endurance of the platform.