{"product_id":"fossil-sport-41mm-gen-4-replacement-battery-385v-350mah-li-polymer","title":"Fossil Sport 41mm Gen 4 Replacement Battery 3.85V 350mAh","description":"\u003cdiv class=\"bpw-desc\"\u003e\n  \u003ch2 class=\"bpw-desc-h2\"\u003eFossil Sport 41mm Gen 4 — 3.85V Li-Polymer Replacement Battery (APP00286)\u003c\/h2\u003e\n\n  \u003cp class=\"bpw-desc-lead\"\u003eThis 3.85V, 350mAh lithium-polymer cell is a direct replacement for the Fossil Sport 41mm Gen 4 smartwatch. It fits the internal battery cavity using the original dimensions of 28.20 x 23.50 x 4.30mm and connects to the existing flex ribbon. Replace it when your watch no longer holds charge through the day or fails to power on.\u003c\/p\u003e\n\n  \u003cul class=\"bpw-desc-bullets\"\u003e\n    \u003cli\u003e\n\u003cstrong\u003eSport 41mm Gen 4 fitment:\u003c\/strong\u003e\n    This cell matches the voltage rail and physical footprint the Gen 4 platform requires. The BMS on the Snapdragon Wear board expects a 3.85V nominal cell — fitting a lower-voltage cell causes the fuel gauge IC to report incorrect state-of-charge from the first boot.\u003c\/li\u003e\n\n    \u003cli\u003e\n\u003cstrong\u003eBench tested on actual hardware:\u003c\/strong\u003e\n    We cycled this cell through charge and discharge on a Gen 4 board, confirmed the BMS accepted the cell without a protection fault, and verified the fuel gauge stabilised after one full charge cycle from near-zero.\u003c\/li\u003e\n\n    \u003cli\u003e\n\u003cstrong\u003ePost-swap charge protocol:\u003c\/strong\u003e\n    After fitting this cell, place the watch on its magnetic charger immediately and run it to 100% before first use. The fuel gauge IC on this platform cannot calibrate its reference point without a full charge cycle following a cell swap — skipping this step causes persistent 0% readings.\u003c\/li\u003e\n  \u003c\/ul\u003e\n\n  \u003chr class=\"bpw-desc-divider\"\u003e\n\n  \u003ch3 class=\"bpw-desc-h3\"\u003eWhy the Sport 41mm Gen 4 shows erratic percentages after a battery swap\u003c\/h3\u003e\n\n  \u003cp class=\"bpw-desc-p\"\u003eThe Gen 4 uses a coulomb-counting fuel gauge tied to the original cell's charge history. When you remove the old cell, that reference is wiped. The IC starts estimating state-of-charge from zero context, so it often reports 0%, 1%, or jumps erratically in the first few hours. This is not a fault with the replacement cell. A full charge cycle from near-depletion to 100% gives the IC enough data to recalibrate — after that, percentage readings stabilise.\u003c\/p\u003e\n\n  \u003ch3 class=\"bpw-desc-h3\"\u003eBattery draining in one day instead of multi-day after swap\u003c\/h3\u003e\n  \u003cp class=\"bpw-desc-p\"\u003eAlways-on display mode combined with continuous heart rate polling is the most common cause of single-day drain on the Gen 4. The heart rate sensor runs a constant optical draw that compounds quickly when the display never sleeps. Check the Fossil app and disable always-on display, then set heart rate monitoring to periodic rather than continuous. Continuous HR alone can pull the 350mAh cell down to 3.5V within 18 hours under normal use.\u003c\/p\u003e\n\u003c\/div\u003e","brand":"BatteryWeb","offers":[{"title":"Warranty 1 Year","offer_id":43416153292890,"sku":"BWCS-FTS414SH-1","price":38.99,"currency_code":"USD","in_stock":true},{"title":"Warranty 2 Year","offer_id":43416153325658,"sku":"BWCS-FTS414SH-2","price":45.99,"currency_code":"USD","in_stock":true},{"title":"Warranty 3 Year","offer_id":43416153358426,"sku":"BWCS-FTS414SH-3","price":49.99,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0674\/4775\/0746\/files\/BW-CS-FTS414SH-1.webp?v=1779760505","url":"https:\/\/batteryweb.com\/products\/fossil-sport-41mm-gen-4-replacement-battery-385v-350mah-li-polymer","provider":"BatteryWeb","version":"1.0","type":"link"}