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Bolt Jr+ Encoder Battery Failure — Silent Position Loss

DANGEROUS CONFIRMED BOLT JR+

Summary

The Bolt Jr+ (RV-13) uses rechargeable batteries to retain encoder positions when the robot is powered off. These batteries fail after 2–3 years of use, or sooner if the robot has been in storage. Flair 6 gives no warning at all when the batteries are depleted — the rig simply loses its reference positions silently. Flair Classic and Flair 7 show the warning: "Robot encoder battery voltage is low or has a fault and should be replaced." Failed batteries mean encoder positions are lost, and the robot cannot be used without first resetting encoder positions. Keeping a spare battery set on hand is essential.

DANGEROUS — Can strand a rig on set

A Bolt Jr+ that has been in storage for several months may arrive on set with dead encoder batteries and no valid positions. If you are using Flair 6, there is no warning — the first sign of failure may be a rig that refuses to move or moves to unexpected positions. Upgrade to Flair Classic or Flair 7 and carry a spare battery set.

Symptoms

  • Rig refuses to move, or moves to unexpected/incorrect positions after power-on
  • Flair Classic / Flair 7 warning: "Robot encoder battery voltage is low or has a fault and should be replaced."
  • Flair 6: no warning — failure is silent
  • Rig has been unused for several months or is 2–3 years old

Systems Affected

  • Bolt Jr+ (RV-13) — all units
  • Not applicable to original Bolt Jr (Staubli), Bolt X, or Cinebot series

Battery Model

MR-BAT6V1 — rechargeable battery packs. These are a standard part and can usually be sourced locally by searching the code. Contact MRMC if you have difficulty.

Background

The Bolt Jr+ arm manufacturer (Mitsubishi Electric, RV-13 series) recommends replacing encoder batteries yearly. MRMC's experience in practice is that 2–3 years is more realistic depending on use and charging cycles — similar to how a mobile phone battery degrades over time.

Extended storage without power is particularly hard on the batteries. If the robot has not been powered on for several months, assume the batteries may be dead and check before arriving on set.

"The batteries are in fact rechargeable batteries so much like a mobile phone battery will deteriorate depending on how it's used and re-charged, the same principle applies here." — Gordon (MRMC), 2023-09-26

"Also if your robot is 2-3 years old and has not been used for some months or is in storage, your encoder batteries are likely already gone bad and have lost their positions. This means you will need to reset the encoder positions before the robot is usable." — Gordon (MRMC), 2024-09-16

Fix

Step 1 — Attempt recharge first

If you receive the low battery warning and replacement batteries are not available:

  1. Leave the robot powered on for an extended period — overnight is recommended.
  2. The batteries will attempt to recharge while the robot is on.
  3. If the fault clears, the batteries have recharged successfully.
  4. If the error persists after an overnight charge, the batteries must be replaced.

"In the first instance, if feasible, leave the robot powered on for an extended period like overnight for example to attempt to recharge the batteries. If the fault clears, that would seem to indicate that the batteries have been recharged." — Gordon (MRMC)

Step 2 — Replace the batteries

  1. Obtain the correct battery model: MR-BAT6V1.
  2. Follow the replacement procedure from the MRMC document: BoltJnrPlusEncoderBatteries.pdf (supplied with your rig as a physical or digital document). MRMC entered liquidation in May 2026 — if you do not have the document, ask in the Flair Community WhatsApp group as other operators may have a copy.
  3. After replacing, allow a charge period before expecting the error to clear.
  4. Replace your spares kit immediately after using the spare set — do not let the spares kit run empty.

"Once you replace them, be sure to remember to replenish your spares kit so that you're not caught out!" — Gordon (MRMC)

Step 3 — If batteries were fully dead (positions lost)

If the encoder batteries discharged completely during storage, encoder positions will have been lost. You will need to reset the encoder positions before the robot is usable. Contact MRMC support for the reset procedure if it is not in your documentation.

Flair 6 Warning

Flair 6 gives NO low battery warning

If you are still using Flair 6 on a Bolt Jr+, there is no encoder battery warning at all. The first indication of failure will be incorrect or missing positions. Upgrade to Flair Classic or Flair 7 to receive the warning message in time to act.

"If you are using Flair 6 for some reason on the Bolt Jnr+ then please consider upgrading to Flair Classic or Flair 7 since Flair 6 will not give the low encoder battery warning." — Gordon (MRMC), 2024-09-16

Prevention

  • Replace batteries proactively after 2–3 years, even without a warning.
  • If the robot has been in storage for several months, check and/or replace batteries before the job.
  • Always carry at least one spare set (MR-BAT6V1). MRMC supplies these, and they are also generally available through other suppliers.
  • Power on the robot regularly during storage to keep batteries topped up.

Source: talk.mrmoco.com — Bolt Jnr+ (RV-13) Encoder batteries — Posts by Gordon (MRMC), 2023-09-26 through 2025-07-09

Official Documentation

Bolt Jr+ Quick Start Guide — Section: Encoder and Position Setup

Revision History

Date Change Editor
2026-05-29 Initial extraction from forum topic 1398 Tom D / Claude Code