I am trying to find a way to open this lock to replace battery
No gurantee, but see those little holes around the collar on the back handle? You can see two of them in your photo. Those often either (a) give a tool a grip to unlock &amp; unthread the collar, allowing you access to full disassembly or (b) require insertion of a tool to release a spring that keeps the collar in place. that would be my starting point.