{"product_id":"tp-link-neffos-c9-replacement-battery-38v-3650mah-li-polymer","title":"TP-Link Neffos C9 Replacement Battery NBL-40A3730 3.8V 3650mAh","description":"\u003cdiv class=\"bpw-desc\"\u003e\n  \u003ch2 class=\"bpw-desc-h2\"\u003eTP-Link Neffos C9 \/ TP707A — 3.8V Li-Polymer Replacement Battery (NBL-40A3730)\u003c\/h2\u003e\n\n  \u003cp class=\"bpw-desc-lead\"\u003eThis is a 3.8V, 3650mAh lithium-polymer replacement battery for the TP-Link Neffos C9 and TP707A smartphones. It replaces the original NBL-40A3730 cell when the factory battery no longer holds adequate charge. Dimensions are 87.26 × 64.52 × 3.80mm — verify clearance before installation.\u003c\/p\u003e\n\n  \u003cul class=\"bpw-desc-bullets\"\u003e\n    \u003cli\u003e\n\u003cstrong\u003eNeffos C9 and TP707A compatibility:\u003c\/strong\u003e\n    Both the Neffos C9 and TP707A share the same battery bay dimensions, connector pinout, and BMS handshake protocol. The NBL-40A3730 part number covers both variants — no hardware modification required.\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 the C9 platform. The BMS accepted the cell without fault flags, and the charge IC completed a full CC\/CV charge cycle to 4.35V without thermal interruption.\u003c\/li\u003e\n\n    \u003cli\u003e\n\u003cstrong\u003eFuel gauge recalibration on first use:\u003c\/strong\u003e\n    After installing a new cell, disable fast charging for the first complete discharge-charge cycle. This lets the fuel gauge IC map the new cell's discharge curve before high-current charging pushes current into an uncalibrated state — reducing the chance of erratic percentage readings early on.\u003c\/li\u003e\n  \u003c\/ul\u003e\n\n  \u003chr class=\"bpw-desc-divider\"\u003e\n\n  \u003ch3 class=\"bpw-desc-h3\"\u003eWhy the Neffos C9 reports wrong battery percentage after a cell swap\u003c\/h3\u003e\n\n  \u003cp class=\"bpw-desc-p\"\u003eThe Neffos C9 uses a coulomb counter in the fuel gauge IC that builds a charge model against the original cell's internal resistance curve. Swap in a new cell and that model no longer matches — the IC reports percentage against old data, not the new cell's actual state of charge. This shows up as large jumps in percentage, or the phone reporting full charge well before 4.35V is reached. One complete discharge to auto-shutoff followed by a full uninterrupted charge resets the coulomb counter baseline against 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 is a voltage cliff, not a capacity fault. When the modem transmits or the screen peaks brightness, instantaneous current draw causes the cell voltage to sag below the BMS cutoff threshold — even if the fuel gauge still shows charge remaining. A new cell with an uncalibrated fuel gauge IC makes this worse because the reported percentage does not reflect true state of charge. Run one full discharge-charge cycle without fast charging to recalibrate the gauge. If the shutdown point migrates down toward 10–15% after two or three cycles, the calibration has corrected.\u003c\/p\u003e\n\u003c\/div\u003e","brand":"BatteryWeb","offers":[{"title":"Warranty 1 Year","offer_id":43391941476442,"sku":"BWCS-TPC900SL-1","price":26.99,"currency_code":"USD","in_stock":true},{"title":"Warranty 2 Year","offer_id":43391941509210,"sku":"BWCS-TPC900SL-2","price":29.99,"currency_code":"USD","in_stock":true},{"title":"Warranty 3 Year","offer_id":43391941541978,"sku":"BWCS-TPC900SL-3","price":32.99,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0674\/4775\/0746\/files\/BW-CS-TPC900SL-1.webp?v=1779142695","url":"https:\/\/batteryweb.com\/products\/tp-link-neffos-c9-replacement-battery-38v-3650mah-li-polymer","provider":"BatteryWeb","version":"1.0","type":"link"}