Changing the battery of the SYE Chronographs is really standard. You, or your local watchmaker, will have to remove the 4 screws maintaining the caseback. You will then have access to the Seiko meca-quartz movement and the battery. Then simply swap the battery with a new one. Seiko recommends using a Seizaiken SR936SW battery. You can also use a Renata 394 type battery. The compatible characteristics are: Silver oxide battery 1.55 V Diameter: 9.5 x thickness: 3.6 (mm)