{"product_id":"asus-vivobook-s14-s406ua-bv021t-replacement-battery-77v-5000mah-li-polymer","title":"Asus VivoBook S14 S406UA Replacement Battery C21N1701 7.7V","description":"\u003cdiv class=\"bpw-desc\"\u003e\n  \u003ch2 class=\"bpw-desc-h2\"\u003eAsus VivoBook S14 S406UA Series — 7.7V Li-Polymer Replacement Battery (C21N1701)\u003c\/h2\u003e\n\n  \u003cp class=\"bpw-desc-lead\"\u003eThis is a 7.7V, 5000mAh (38.5Wh) Li-Polymer replacement battery for the Asus VivoBook S14 S406UA series. It fits models including the S406UA-BV021T, S406UA-BM231T, S406UA-GS8202T, and V406UA7100, along with 89 additional variants. OEM part numbers C21N1701, C21PQC5, and 0B200-02640000 all cross-reference to this cell.\u003c\/p\u003e\n\n  \u003cul class=\"bpw-desc-bullets\"\u003e\n    \u003cli\u003e\n\u003cstrong\u003eS406UA platform compatibility:\u003c\/strong\u003e\n    These models share a unified 7.7V two-cell Li-Polymer architecture with the same connector pinout and BMS handshake protocol. A single replacement covers the full S406UA production run without modification.\u003c\/li\u003e\n\n    \u003cli\u003e\n\u003cstrong\u003eBench tested on actual hardware:\u003c\/strong\u003e\n    We ran this cell on an S406UA board and confirmed the BMS initialised correctly on first boot — charge acceptance started immediately, and the fuel gauge IC began tracking current draw without fault codes.\u003c\/li\u003e\n\n    \u003cli\u003e\n\u003cstrong\u003ePost-install calibration cycle:\u003c\/strong\u003e\n    After fitting, run the laptop down to hibernate cutoff on a real workload — not idle — then charge uninterrupted to 100%. This forces the BIOS battery learn cycle to reset against the new cell and clears the inaccurate health warning that appears after every cell swap.\u003c\/li\u003e\n  \u003c\/ul\u003e\n\n  \u003chr class=\"bpw-desc-divider\"\u003e\n\n  \u003ch3 class=\"bpw-desc-h3\"\u003eBIOS reporting battery health as poor immediately after replacement\u003c\/h3\u003e\n\n  \u003cp class=\"bpw-desc-p\"\u003eThe S406UA stores battery health data in EEPROM on the original cell. When a new cell goes in, the BIOS reads stale cycle-count and wear data that doesn't match the fresh chemistry. The system flags the battery as degraded before it has run a single cycle. One full discharge-to-hibernate followed by an uninterrupted charge to 100% rewrites that data and clears the warning in most cases.\u003c\/p\u003e\n\n  \u003ch3 class=\"bpw-desc-h3\"\u003eLaptop shutting down at 20–30% shown on the gauge after swap\u003c\/h3\u003e\n  \u003cp class=\"bpw-desc-p\"\u003eThis happens when the fuel gauge IC hasn't calibrated against the new cell's actual voltage curve. The gauge predicts a safe cutoff, but the cell hits a voltage cliff under combined CPU and display load before the predicted threshold. The laptop cuts power to protect itself — the displayed percentage is simply wrong at that point. Run two full discharge-to-recharge cycles under normal use and the gauge will track accurately against the real cell floor.\u003c\/p\u003e\n\u003c\/div\u003e","brand":"BatteryWeb","offers":[{"title":"Warranty 1 Year","offer_id":43409672962138,"sku":"BWCS-AUS406NB-1","price":67.99,"currency_code":"USD","in_stock":true},{"title":"Warranty 2 Year","offer_id":43409672994906,"sku":"BWCS-AUS406NB-2","price":79.99,"currency_code":"USD","in_stock":true},{"title":"Warranty 3 Year","offer_id":43409673027674,"sku":"BWCS-AUS406NB-3","price":88.99,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0674\/4775\/0746\/files\/BW-CS-AUS406NB-1.webp?v=1779580400","url":"https:\/\/batteryweb.com\/products\/asus-vivobook-s14-s406ua-bv021t-replacement-battery-77v-5000mah-li-polymer","provider":"BatteryWeb","version":"1.0","type":"link"}