admin Encoder battery replacement is one of the most critical preventive maintenance tasks on a servo press. A depleted battery causes absolute position loss, requiring homing and potentially causing production downtime. ## Battery Types by Drive Brand | Drive Brand | Battery Part | Voltage | Typical Life | |-------------|-------------|---------|--------------| | Fanuc | A98L-0031-0012 | 3.6V Li | 3-5 years | | Siemens S120 | 6SY7000-0AB36 | 3.6V Li | 3-5 years | | Yaskawa Sigma-7 | JZSP-BA01 | 3.6V Li | 3-5 years | | Mitsubishi MR-J4 | MR-BAT6V1SET | 3.6V Li | 3-5 years | | ABB | 3HAC044075-001 | 3.6V Li | 3-5 years | ## Critical Rule: Replace with Power ON **Never replace encoder battery with power off.** The encoder uses battery power to retain absolute position data when main power is off. If you disconnect the battery with power off, position data is lost and homing is required. Correct procedure: 1. Power on the servo system 2. Disconnect old battery 3. Connect new battery within 30 seconds 4. Verify no position loss alarm ## Replacement Procedure (Fanuc Example) 1. Power on CNC and servo system 2. Navigate to SYSTEM > DIAGNOSIS > BATTERY to confirm battery voltage (should be >3.0V; replace if <3.1V) 3. Locate battery on servo motor (small connector near encoder) 4. Disconnect old battery 5. Connect new battery immediately 6. Verify alarm 306 (battery voltage zero) does not appear 7. Document replacement in maintenance log ## Preventive Schedule Replace encoder batteries every **3 years** regardless of voltage reading. Battery voltage can appear normal until sudden failure. Add to annual PM checklist: - Year 1: Check voltage, document - Year 2: Check voltage, document - Year 3: Replace all encoder batteries - Repeat cycle ## Warning Signs - AL.92 (Mitsubishi) or alarm 306 (Fanuc): battery warning ??replace within 1 week - Position drift after power cycle: battery may be failing - Intermittent homing required: battery near end of life
admin Related: see also [Mitsubishi MR-J4 AL.E3 absolute position lost](https://servopress.club/d/137-137-mitsubishi-mr-j4-al-e3-alarm-absolute-position-lost-on-servo-press) for complementary detail.