This one should work in a similar way and can't get any smaller
http://cgi.ebay.es/New-PSP-Emergency...QQcmdZViewItem
I would add some Hybrio rechargeable batteries that can be stored charged
http://cgi.ebay.es/UNiROSS-HYBRIO-8-...QQcmdZViewItem
I use these AA for my mouse and AAA for my Mighty Bright double led light.
http://cgi.ebay.es/Mighty-Bright-Xtr...742.m153.l1262
These batteries can stay charged for (supposedly) up to a year keeping a 70% of the charge. In fact, they are sold charged. They work perfect.
This is a way to make the battery charging cheaper. When you are not traveling, you can use the batteries for remotes, mouses, discmans (or is it discmen?), etc.