About this replacement
Garmin vivoactive 4S 40mm — 3.8V Li-Polymer Replacement Battery (361-00096-01)
This 3.8V, 130mAh lithium-polymer cell is a direct swap for the original 361-00096-01 battery inside the Garmin vivoactive 4S 40mm smartwatch. It fits the 40mm case only — not the larger vivoactive 4 44mm variant. Dimensions are 26.30 × 16.40 × 3.90mm, matching the original cell footprint.
- vivoactive 4S 40mm fitment: The 40mm and 44mm vivoactive 4 housings use physically different cells with different footprints and connector positions. This cell is sized and wired for the 40mm chassis only. Fitting it into the 44mm body is not possible without modification.
- Bench tested on actual hardware: We cycled this cell through charge and discharge on the vivoactive 4S platform. The BMS accepted the cell without error flags, fuel gauge initialised correctly after a full charge, and the heart rate and GPS sensors drew current within expected parameters.
- Post-swap charge cycle: After fitting this cell, place the watch on its magnetic charger immediately and charge it to 100% before first use. The fuel gauge IC on the vivoactive 4S loses its reference point when the cell is swapped — it cannot recalibrate accurately without a complete charge cycle starting from near-zero.
Why the vivoactive 4S shows 0% immediately after a battery swap
The vivoactive 4S uses a fuel gauge IC that tracks charge state by measuring cumulative current flow over time. When you disconnect the old cell, that reference is wiped. The IC has no memory of the new cell's state of charge, so it defaults to 0% or powers off entirely. This is not a fault with the replacement cell. Place the watch on charge immediately after assembly and let it reach 100% — the IC re-establishes its reference during that first full charge cycle and will read accurately from that point forward.
Battery draining in one day instead of the expected multi-day window
Always-on display mode combined with continuous heart rate monitoring is the most common cause of single-day drain on the vivoactive 4S. Together, these two features can draw enough current to deplete a 130mAh cell significantly faster than Garmin's quoted figures, which assume display-on-gesture and periodic HR sampling. Check Settings → Display and confirm always-on is off, then set heart rate to Smart recording rather than Every Second. If drain continues after those changes, check which third-party watch faces are installed — some poll sensors continuously in the background.