27/06/2026 8:38 am
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Automotive Q&A
2018 Volvo XC60 says Start/Stop service required but the main battery tests well
Review the evidence, add a focused answer, and distinguish confirmed measurements from assumptions.
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The main AGM battery is fully charged and passes conductance and load tests. Start/stop remains unavailable, and scan data shows the support battery dropping to 9.8 V during a wake event while the main battery stays above 12.3 V. The DC/DC support circuit has no current fault.
Is the small support battery enough to cause the message, and should both batteries be registered?
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28/06/2026 6:14 am
Use the wiring and battery-management procedure for the exact platform. Load-test the support battery separately and verify its fuse, ground and charging voltage. A weak support battery can disable start/stop even when the main battery is healthy. Registration or reset requirements may differ for the two batteries, so follow the replacement procedure rather than applying a generic battery reset.
After replacement, confirm the support battery accepts charge and the module sees plausible voltage through multiple sleep and wake cycles.
Topic starter
29/06/2026 8:45 am
The support battery fell below its load-test limit while its cables dropped less than 0.1 V. Replacing it and performing the specified battery-monitor procedure restored start removed link Both battery voltages remained stable on the next wake test.