When an ABB robot powers up reporting that its revolution counters are not updated, the first thing we check is the battery on the serial measurement board (SMB). It makes no difference whether it is an S4C+ with a long service life behind it or a freshly installed OmniCore. In almost every case the battery has run flat or been disconnected while the robot was unpowered, and the controller no longer knows which motor revolution each axis is on.
What the SMB battery does and why it sits in the arm
The SMB battery lives in the manipulator, not in the cabinet. It powers the measurement board while the robot is de-energised so the axis revolution counters are not lost. The motor feedback device knows its position within one turn. How many turns each axis has made is held by the board, and that count only survives while the board stays powered. With the cabinet on, there is no issue; with the cabinet off, everything rests on the battery. The principle is identical on S4, S4C, S4C+, IRC5 and OmniCore.
One mix-up we see regularly involves the computer battery. The controller also carries this battery, which keeps the clock and motherboard settings, and it has nothing to do with revolution counters. If someone has already replaced the battery in the cabinet and the robot keeps losing its counters, the one failing is in the arm.
Which controller messages point to the battery
On IRC5 the message is event 20032, «Rev. counter not updated», described as «One or several absolute measurement axes are not synchronized». On other generations the symptom and the fix are the same. The event number and exact wording, however, must be checked in the documentation for that system: do not assume they match IRC5.
There is usually an earlier warning. ABB Product Manuals, for instance those for the IRB 6700 or IRB 7600, list event 38213, «Battery charge low». It means the battery is due for replacement, not that the counters are already gone.
A third message often gets lumped in with these: 50057, «Joint not synchronized». On IRC5 it means an axis position after shutdown or power loss is too far from where it was before. Updating the revolution counters clears it too, but it does not indicate a flat battery. The usual cause is that the axis moved while the robot was unpowered, for instance because someone shifted it by hand. If you get a 50057 with a healthy battery, find out what moved that axis before closing the case.
Why a low-battery warning cannot wait
As long as the controller is powered, a low battery does no harm, because the board is fed from the cabinet. Trouble starts at the first power-down, whether that is a mains outage, a weekend with the main breaker off, the summer shutdown or someone switching off the cell to work on the tooling. When power returns, the robot has lost its revolution counters and will not run in automatic until they are updated.
That is why ABB recommends keeping the controller powered until the moment of replacement, so synchronisation is not lost. In practice, as soon as the warning appears, the shift handover notes should state that this cabinet stays on. The swap is then scheduled for the next planned stop, with the battery already on the shelf.
Which battery each robot in your ABB fleet uses
The function is the same from S4 to OmniCore; the battery is not. It changes with the robot's era and, on IRC5 and OmniCore, with the measurement board fitted to each model. There are several types, with different formats and connectors, and they are not interchangeable. Ordering «the SMB battery for an ABB» with no further detail is the quickest way to receive one that does not fit.
Before ordering:
- Open the measurement board cover on the manipulator and check which board and battery are actually fitted. Do not rely on the robot next to it, even if it is the same model.
- Cross-check against the spare parts documentation in that model's Product Manual, which is where the correct part number is listed.
- Record the part number in your CMMS against the robot serial number, not the model: in a fleet with years of repairs behind it, units can differ.
On S4, S4C and S4C+ this check matters even more. Often nobody has opened that cover in years, and what is inside may not be the original fit.
How often to replace the SMB battery
The manufacturer's interval depends on the model. Check it in each robot's Product Manual, under the task «Replacing the SMB battery». No single figure applies across a whole fleet.
Our rule is simpler: on the ABB robots we maintain, we replace it every 24 months without waiting for the warning. This is a PAS criterion, not the manufacturer's, and it is driven by downtime cost. A flat battery turns a job of minutes into updating revolution counters, or recalibrating, with the robot stopped. A single interval also tidies up the plan: every ABB in the plant, S4C+ or OmniCore, runs on the same cycle and gets grouped into the same stop.
How to plan the replacement
- Identify the battery for each robot and have it in stock before the stop.
- Book the job into a planned stop, not a scramble after a warning on a Friday afternoon.
- Until then, do not power down any controller showing a low-battery warning.
- Carry out the replacement following the model's Product Manual.
- On start-up, confirm there is no revolution counter or battery warning before returning the robot to production.
- Log the date and part number for the next cycle.
Already tripped: update the counters or recalibrate?
If the battery has run flat, the mechanics have not changed; only the turn count has been lost. The fix is to update the revolution counters by bringing each axis to its synchronisation mark as described in the robot manual. This is not a calibration, and if nothing has touched the mechanics, no calibration tooling is needed.
- Replace the battery first. If you update with the old one, you will lose the counters again at the next power-down.
- Bring each axis to its mark carefully. An axis updated one motor revolution off its mark raises no error: you get a robot that starts normally and misses its points.
- Before going back to automatic, check known positions, such as a reference point in the program or the TCP on a fixed fixture.
- If the robot has taken a hit, or doubts about position remain after the update, you are into calibration. We cover it in mastering and axis calibration.
In our ABB robot maintenance visits we identify the battery on every robot, from S4 to OmniCore, and log it with its replacement date in the preventive maintenance plan. If your event log already shows battery warnings, that is the first thing we deal with at the next stop.