As previously posted:
Polymer Lithium Ion Battery - 1000mAh 3.7V
Dimensions: 2.09 x 1.3 x 0.225" (53 x 33 x 5.7 mm)
$11.95, not in stock but backorders are allowed.
http://www.sparkfun.com/products/339
I will certainly want to replace mine when it is needed rather than getting a new reader (with features I like less) or using an external battery pack.
What folks see in the newer touch screen wireless readers is beyond me because I live & work in a rural area & none of that internet stuff does me a whisker of good.
Not only that - my EZ Reader is perfect just as it is & needs nothing right now.