Power Extender

Power Extender is a backup power supply for different types of PDAs. Doesn't look too big so wouldn't be burdensome to carry when travelling. If they continue to provide new adapters it will also not become redundant when you change your PDA. Pocket Games looks like a very good site to buy useful accessories like this. They also claim 'we export almost anything' so is a good option for people outside Japan who wanted to get hold of products only available here.