EXFO Optical Power Expert User Manual page 62

Maintenance
Replacing the Battery
Electrostatic discharge (ESD) damage can cause complete or
intermittent equipment failures.
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Always use an ESD-preventive wrist or ankle strap when
replacing the battery. Ensure that the antistatic strap makes
good skin contact and that the end of its wire is grounded
properly.
Never touch any component inside the unit other than those
identified in the procedure hereafter, either with tools or your
fingers.
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AUTION
PX1