{"product_id":"apple-watch-38mm-replacement-battery-38v-200mah-li-polymer","title":"Apple Watch 38mm A1578 Replacement Battery 3.8V 200mAh","description":"\u003cdiv class=\"bpw-desc\"\u003e\n  \u003ch2 class=\"bpw-desc-h2\"\u003eApple Watch 38mm — 3.8V Li-Polymer Replacement Battery (A1578)\u003c\/h2\u003e\n\n  \u003cp class=\"bpw-desc-lead\"\u003eThis is a 3.8V, 200mAh Li-Polymer cell that replaces the original A1578 battery inside the Apple Watch 38mm. It also fits the Watch 42mm and models A1553 and A1554. Swap it in when the original cell no longer holds a charge across a full day of use.\u003c\/p\u003e\n\n  \u003cul class=\"bpw-desc-bullets\"\u003e\n    \u003cli\u003e\n\u003cstrong\u003e38mm and 42mm fitment:\u003c\/strong\u003e\n    Both watch sizes use the same A1578 cell spec — same voltage rail, same connector pinout, and the same BMS handshake with the S1 or S1P processor module. One part covers both.\u003c\/li\u003e\n\n    \u003cli\u003e\n\u003cstrong\u003eBench tested on actual hardware:\u003c\/strong\u003e\n    We ran this cell on a Watch 38mm unit and confirmed the BMS accepted the new cell without fault codes. The fuel gauge IC initialised correctly after a full charge cycle from near-zero.\u003c\/li\u003e\n\n    \u003cli\u003e\n\u003cstrong\u003ePost-swap charging requirement:\u003c\/strong\u003e\n    After fitting this cell, place the watch on its magnetic charger immediately and charge to 100% before first use. The fuel gauge IC on the Watch platform loses its voltage reference when the old cell is removed — without a full charge cycle from near-zero, the percentage readout will be inaccurate and the watch may shut down unexpectedly at mid-charge levels.\u003c\/li\u003e\n  \u003c\/ul\u003e\n\n  \u003chr class=\"bpw-desc-divider\"\u003e\n\n  \u003ch3 class=\"bpw-desc-h3\"\u003eWhy the Apple Watch BLE session drops after a battery swap\u003c\/h3\u003e\n  \u003cp class=\"bpw-desc-p\"\u003eRemoving the battery cuts power to the W1 or W2 wireless chip, which discards its active Bluetooth session with the paired iPhone. The watch reboots as an unknown peripheral. The iPhone holds the old pairing record but the watch no longer matches it. Re-pair through the Watch app on the iPhone — Settings → General → Reset → Erase Apple Watch Content and Settings — then set up as new.\u003c\/p\u003e\n\n  \u003ch3 class=\"bpw-desc-h3\"\u003eWatch draining to zero within one day after cell replacement\u003c\/h3\u003e\n  \u003cp class=\"bpw-desc-p\"\u003eIf battery life collapses to under 24 hours after the swap, always-on display combined with continuous heart rate polling is usually the cause. The new cell has a slightly different internal impedance than the aged original, and the sensor stack draws harder against it during the first several charge cycles until the BMS recalibrates. Check that Theatre Mode and Wrist Detection are both enabled, then run three full charge-to-discharge cycles. If drain persists past cycle three, confirm the display assembly was reseated fully — a lifted gasket keeps the screen backlight at full draw.\u003c\/p\u003e\n\u003c\/div\u003e","brand":"BatteryWeb","offers":[{"title":"Warranty 1 Year","offer_id":43416174428250,"sku":"BWCS-IPW153SH-1","price":25.99,"currency_code":"USD","in_stock":true},{"title":"Warranty 2 Year","offer_id":43416174461018,"sku":"BWCS-IPW153SH-2","price":28.99,"currency_code":"USD","in_stock":true},{"title":"Warranty 3 Year","offer_id":43416174493786,"sku":"BWCS-IPW153SH-3","price":31.99,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0674\/4775\/0746\/files\/BW-CS-IPW153SH-1.webp?v=1779760588","url":"https:\/\/batteryweb.com\/products\/apple-watch-38mm-replacement-battery-38v-200mah-li-polymer","provider":"BatteryWeb","version":"1.0","type":"link"}