{"product_id":"apple-iwatch-series-4-40mm-replacement-battery-385v-220mah-li-polymer","title":"Apple iWatch Series 4 40mm A2058 3.85V Replacement Battery","description":"\u003cdiv class=\"bpw-desc\"\u003e\n  \u003ch2 class=\"bpw-desc-h2\"\u003eApple iWatch Series 4 40mm — 3.85V Li-Polymer Replacement Battery (A2058)\u003c\/h2\u003e\n\n  \u003cp class=\"bpw-desc-lead\"\u003eThis is a 3.85V, 220mAh Li-Polymer cell replacing part number A2058 in the Apple iWatch Series 4 40mm. It fits models A1975, A1977, and A2007 — all 40mm Series 4 variants sharing the same battery bay and connector. Swapping this cell restores the watch's ability to run fitness tracking, heart rate monitoring, and notifications at full capacity.\u003c\/p\u003e\n\n  \u003cul class=\"bpw-desc-bullets\"\u003e\n    \u003cli\u003e\n\u003cstrong\u003eSeries 4 40mm compatibility:\u003c\/strong\u003e\n    The A1975, A1977, and A2007 model numbers cover GPS, GPS + Cellular, and regional variants of the 40mm Series 4. All share the same 23.80 × 18.92 × 4.44mm battery footprint, the same flex connector, and the same BMS communication protocol — one cell covers the entire 40mm Series 4 lineup.\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 Series 4 unit, confirmed BMS handshake on reconnect, and verified the fuel gauge IC accepted the new cell without throwing a service warning on the watch face.\u003c\/li\u003e\n\n    \u003cli\u003e\n\u003cstrong\u003eFuel gauge calibration after swap:\u003c\/strong\u003e\n    Place the watch on its magnetic charger immediately after fitting this cell and charge to 100% before powering the device on. The Series 4 fuel gauge IC loses its reference point when the original cell is removed — skipping this step causes the percentage readout to jump or read incorrectly from the first boot.\u003c\/li\u003e\n  \u003c\/ul\u003e\n\n  \u003chr class=\"bpw-desc-divider\"\u003e\n\n  \u003ch3 class=\"bpw-desc-h3\"\u003eWhy the Series 4 shows a service alert after a battery swap\u003c\/h3\u003e\n  \u003cp class=\"bpw-desc-p\"\u003ewatchOS includes a battery health check that flags replacement cells until the fuel gauge IC completes a full calibration cycle. The alert appears in Settings → Battery → Battery Health and typically reads as \"Unable to determine battery health.\" This is a calibration state, not a fault. Running one full charge from near-zero to 100% and then using the watch until it prompts a charge clears the flag in most cases.\u003c\/p\u003e\n\n  \u003ch3 class=\"bpw-desc-h3\"\u003eWatch not pairing with iPhone after battery replacement\u003c\/h3\u003e\n  \u003cp class=\"bpw-desc-p\"\u003eRemoving the battery terminates the active BLE session between the watch and the paired iPhone. When the watch reboots with a new cell, the phone-side Bluetooth stack does not automatically re-establish the link. Open the Watch app on the iPhone, go to General → Reset, and select \"Reset Network Settings\" on the watch — this clears the stale session. After that, keep the watch and phone within one metre until the pairing indicator confirms connection.\u003c\/p\u003e\n\u003c\/div\u003e","brand":"BatteryWeb","offers":[{"title":"Warranty 1 Year","offer_id":43416169742426,"sku":"BWCS-IPW205SH-1","price":24.99,"currency_code":"USD","in_stock":true},{"title":"Warranty 2 Year","offer_id":43416169775194,"sku":"BWCS-IPW205SH-2","price":27.99,"currency_code":"USD","in_stock":true},{"title":"Warranty 3 Year","offer_id":43416169807962,"sku":"BWCS-IPW205SH-3","price":30.99,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0674\/4775\/0746\/files\/BW-CS-IPW205SH-1.webp?v=1779760548","url":"https:\/\/batteryweb.com\/products\/apple-iwatch-series-4-40mm-replacement-battery-385v-220mah-li-polymer","provider":"BatteryWeb","version":"1.0","type":"link"}