About this replacement
Garmin Approach S10 / Forerunner 35 — 3.7V Li-Polymer Replacement Battery (361-00117-00)
This is a 3.7V, 180mAh lithium-polymer cell that replaces the original battery in the Garmin Approach S10, Approach S20, and Forerunner 35. All three watches share the same cell format, OEM part number, and connector. Dimensions are 29.00 × 19.42 × 3.38mm — confirm clearance before ordering if your unit has any aftermarket housing.
- Approach S10, S20, and Forerunner 35 compatibility: These three models share the same PCB layout, JST connector pitch, and battery bay dimensions. Garmin used the same cell across the platform, so one part number covers all three without any modification.
- Bench tested on actual hardware: We ran this cell on a Forerunner 35 and confirmed the BMS handshake completed correctly — the watch powered on, accepted a charge, and the fuel gauge IC initialised without error flags.
- Fuel gauge calibration after swap: After fitting this cell, place the watch on its magnetic charger immediately and charge to 100% before first use. The fuel gauge IC on these Garmin platforms loses its reference point when the cell is disconnected. Without a full charge cycle from near-zero post-swap, the percentage readout will be inaccurate for days.
Why GPS and continuous tracking drain a 180mAh cell faster than you expect
The Approach S10 runs active GPS acquisition at roughly 25–30mA draw — a significant load on a 180mAh cell. When GPS is active simultaneously with course mapping and step tracking, the battery sees near-peak current continuously. That is by design for a golf round, not a defect. Avoid leaving GPS mode running between holes or in the clubhouse, as the radio stays active until explicitly ended.
Magnetic charge contacts not making connection after reassembly
If the watch shows no charging indicator when placed on its magnetic charger after a battery swap, the rear case has likely shifted fractionally during reassembly, misaligning the charge contacts. Remove the watch from the charger, inspect the two contact points on the case back for debris or adhesive residue, and reseat firmly. If the gap persists, loosen the case screws by a quarter turn, reposition the rear cover flush, then re-tighten and test. The charger LED should respond within 10 seconds of correct contact.