Satechi iCel Extended Battery Pack

[Cancre]

I'm looking for a battery extender and I found this: Satechi iCel Extended Battery Pack and Charger for iPhone 3G & 3Gs, iPod, Flip & Vado Camcorders
$59.99 reg. price $69.99
Also, there is this other one:
IMP500 3G 3Gs iPhone iTouch external battery Free AC charger
List Price: $79.95
Our Price: $58.95
Sale Price: $45.95

Mainly, I want something that I will be able to use on the golf course while my iPhone serves as a GPS with the Golfshot app. Considering what I've read, I'ill be lucky if I can complete an 18 holes round with one charge.
So, what do you think?

Cancre

 

[Earless Puppy]

add a link to the product

 

[Earless Puppy]

there are much smaller ones out there that I would buy first