The K1 has a simple, user replaceable battery. $19.99 from Amazon. Along with a SD card slot, something else they decided to forego with the K2, under the guise of 'improvements'.
You can still find K1's on Ebay, and sometimes here.
edit.......Amazon also sells the refurbished K1's when they have them in stock....full warranty.
http://www.amazon.com/gp/offer-listing/B000FI73MA