Yangdock E-Commerce via Amazon offers the Masione 2,500mAh Ni-Cad Replacement Battery for iRobot Roomba for $16.99. Coupon code "FRMYDEAL" cuts that to $14.44. Plus, Prime members bag free shipping. That's $16 off and the best price we could find. It's compatible with a range of Roomba models (listed on the product page). Deal ends May 12.