Depends on what you're going to do for those 10 hours. Listen to mp3's at low CPU with the screen off? No problem with the extended battery. Surfing the web over wifi? I doubt any battery will last 10 hours.
That said, I got my 2200 mAh extended battery from
Axim Cases - Ultimate Website for Dell Axim Case Shoppers. The biggest battery for the Axim is a massive 3300 mAh one. You'd have to use a travel charger with it, though, as it won't fit in the cradle. I got my spare charger from
BoxWave Accessories - iPhone, BlackBerry, Treo, iPod, PSP & PDA Accessories. Also, a synch cable can charge your Axim, but depending on your battery capacity, you might not be able to charge while it's on. Best bet is a wall charger. Hope this helps.