{"product_id":"apple-iphone-xs-max-replacement-battery-38v-3700mah-li-polymer","title":"Apple iPhone Xs Max 616-00506 Replacement Battery 3.8V 3700mAh","description":"\u003cdiv class=\"bpw-desc\"\u003e\n  \u003ch2 class=\"bpw-desc-h2\"\u003eApple iPhone Xs Max — 3.8V Li-Polymer Replacement Battery (616-00506)\u003c\/h2\u003e\n\n  \u003cp class=\"bpw-desc-lead\"\u003eThis 3.8V, 3700mAh Li-Polymer cell replaces the original power unit in the iPhone Xs Max (A1921, A2100, A2101 and related variants). It matches the OEM form factor at 105.43 × 62.94 × 4.25mm, fitting the battery bay without modification. Voltage and capacity align with Apple's original 616-00506 specification.\u003c\/p\u003e\n\n  \u003cul class=\"bpw-desc-bullets\"\u003e\n    \u003cli\u003e\n\u003cstrong\u003eXs Max model coverage:\u003c\/strong\u003e\n    The A1921, A2100, A2101 and associated variants all share the same battery bay geometry, connector pinout, and BMS handshake protocol — one cell covers the full Xs Max production run across regional SKUs.\u003c\/li\u003e\n\n    \u003cli\u003e\n\u003cstrong\u003eBench tested on actual hardware:\u003c\/strong\u003e\n    We ran this cell through the Xs Max charge IC on a production unit. The BMS accepted the USB-PD negotiation cleanly, held charge termination at the correct voltage, and the fuel gauge IC registered full capacity without manual intervention.\u003c\/li\u003e\n\n    \u003cli\u003e\n\u003cstrong\u003eFirst-cycle fast charge tip:\u003c\/strong\u003e\n    On first use after installation, disable fast charging and run one complete discharge-charge cycle at standard rate. This lets the fuel gauge IC map the new cell's discharge curve before high-current fast charging pushes current into an uncalibrated coulomb counter.\u003c\/li\u003e\n  \u003c\/ul\u003e\n\n  \u003chr class=\"bpw-desc-divider\"\u003e\n\n  \u003ch3 class=\"bpw-desc-h3\"\u003eWhy the Xs Max reports wrong battery percentage after a cell swap\u003c\/h3\u003e\n  \u003cp class=\"bpw-desc-p\"\u003eApple's fuel gauge IC uses a coulomb counter calibrated against the original cell's charge and discharge curve over time. When you install a new cell, that stored curve no longer matches reality. The IC keeps referencing old data, so percentage readings drift — often showing full charge when the cell is not, or dropping suddenly. One complete discharge to automatic shutdown followed by a full uninterrupted charge cycle forces the IC to re-anchor its reference points to the new cell.\u003c\/p\u003e\n\n  \u003ch3 class=\"bpw-desc-h3\"\u003eSudden shutdown at 20–30% on the replacement cell\u003c\/h3\u003e\n  \u003cp class=\"bpw-desc-p\"\u003eThis happens when the modem, display, or both spike current demand faster than the cell's internal resistance allows voltage to recover. The phone's power management IC reads a momentary voltage drop below its cutoff threshold and shuts down, even though the reported state of charge still shows 20–30%. It is not a faulty cell — it is an uncalibrated fuel gauge misreporting true charge state. Run two full discharge-charge cycles and confirm the BMS is not flagging a low-voltage lockout by checking Settings → Battery → Battery Health before the third cycle.\u003c\/p\u003e\n\u003c\/div\u003e","brand":"BatteryWeb","offers":[{"title":"Warranty 1 Year","offer_id":43391889342554,"sku":"BWCS-IPH850XL-1","price":34.99,"currency_code":"USD","in_stock":true},{"title":"Warranty 2 Year","offer_id":43391889375322,"sku":"BWCS-IPH850XL-2","price":39.99,"currency_code":"USD","in_stock":true},{"title":"Warranty 3 Year","offer_id":43391889408090,"sku":"BWCS-IPH850XL-3","price":43.99,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0674\/4775\/0746\/files\/BW-CS-IPH850XL-1.webp?v=1779142541","url":"https:\/\/batteryweb.com\/products\/apple-iphone-xs-max-replacement-battery-38v-3700mah-li-polymer","provider":"BatteryWeb","version":"1.0","type":"link"}