Mitsubishi Electric MELSERVO-J3 Series Handbook page 534

Part 8: Review on Replacement of Optional Peripheral Equipment
(4) Replacement procedure of the built-in battery
When the MR-BAT6V1SET-A reaches the end of its life, replace the built-in MR-BAT6V1 battery.
Cover
Projection
(four places)
1) While pressing the locking part, open the cover.
Tab
2) Replace the battery with a new MR-BAT6V1 battery.
3) Press the cover until it is fixed with the projection of
the locking part to close the cover.
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