When ANT+ Pairing Was Really a Battery-Door Fault

Archive note: Originally published on Mullener in 2015. It describes an early Stages Shimano 6800 unit and its period-specific replacement parts, not current product guidance.

My Stages power meter had begun failing to power on or pair with Garmin head units over ANT+. It could also disappear during a ride and refuse to restart.

The obvious suspect was software. I had recently updated the meter using the Android app, and reports elsewhere described battery drain caused by a Bluetooth transmitter remaining active. But that failure mode did not match what I was seeing.

Following the physical evidence

The retailer first supplied a replacement battery door with a different red O-ring. The fault remained, and the cap did not appear to sit flush against the body of the meter.

Removing the O-ring temporarily changed the behaviour: when the crank woke, both a Garmin 500 and 705 detected the meter immediately. That pointed away from ANT+ pairing and toward pressure on the coin cell. The cap and seal were not holding the battery firmly against both contacts.

Stages had identified the issue and produced a revised cap, stamped 7/15, with a thinner cap and a flatter black seal. Once fitted, the meter returned to reliable operation.

The diagnostic lesson

The visible symptom was wireless—an ANT+ device would not pair—but the underlying fault was mechanical. The radio could not advertise because the unit did not have reliable power.

For intermittent sensor failures, work from the bottom of the stack:

• inspect the enclosure, seals and battery contacts;
• confirm stable power under movement and vibration;
• then investigate firmware, radio pairing and head-unit compatibility;
• change one variable at a time and record what alters the symptom.

It is tempting to debug at the layer where a failure appears. This one was a good reminder to start one layer lower.