There are two round inserts at the bottom of the shaver that cover the two screws needed to open the case. Pry off these covers, unscrew the two screws, pull off the bottom and then slide off the middle part of the case exposing the batteries. They are two Sanyo nickel cadmium KR600AE. I have never bought these here, http://www.wholesalebatteries.us/battery.cfm/hurl/nicd-nimh-cells/all-vendor/nickel-cadmium-nicad-cells/KR600AE.htm, and they are probably available locally.
HOWEVER, the batteries are not snap in but a spot welded or soldered into the shaver. BatteriesPlus, http://www.batteriesplus.com/t-storeloc.aspx, will sell you the batteries and for a nominal charge attach them. The batteries can explode with to much heat so I urge you not to do it yourself.