What is a servo press?

A servo press uses servo motors for precise force and position control during forming operations.

How do I calculate servo press tonnage?

Use our free tonnage calculator at servopress.club/tonnage-calculator.html

Servo Press Encoder Battery Replacement: Procedure and Schedule

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

raj_maintenance

Encoder battery replacement tip: always replace with the press powered on. If you remove the battery with power off, the encoder loses its absolute position immediately. With power on, the encoder runs from the drive power supply while you swap the battery. This is in the manual but I have seen experienced technicians make this mistake.

mike_chen_eng

Encoder battery replacement timing is often overlooked until alarms appear. Most absolute encoders require battery replacement every 3-5 years depending on ambient temperature and duty cycle. Schedule replacements during planned maintenance windows, not reactively. Critical steps: power down the servo axis completely before replacement, verify battery type matches OEM specs exactly, and perform homing cycle immediately after installation. Monitor encoder communication for 24 hours post-replacement. Document battery replacement dates in your maintenance log—this data helps predict future failures and optimize replacement intervals for your specific operating conditions.