{"product_id":"sony-ericsson-u100-replacement-battery-37v-950mah-li-ion","title":"Sony Ericsson U100 BST-43 Replacement Battery 3.7V 950mAh","description":"\u003cdiv class=\"bpw-desc\"\u003e\n  \u003ch2 class=\"bpw-desc-h2\"\u003eSony Ericsson U100 \/ YARI Series — 3.7V Li-ion Replacement Battery (BST-43)\u003c\/h2\u003e\n\n  \u003cp class=\"bpw-desc-lead\"\u003eThis is a 3.7V, 950mAh Li-ion replacement battery for the Sony Ericsson U100, U100i, YARI, and Vulcan. It uses the BST-43 cell spec and fits all handsets in that lineup. Slide it in where the original sits — the connector and footprint match directly.\u003c\/p\u003e\n\n  \u003cul class=\"bpw-desc-bullets\"\u003e\n    \u003cli\u003e\n\u003cstrong\u003eU100 and YARI platform compatibility:\u003c\/strong\u003e\n    These models share the same battery bay dimensions, 3.7V single-cell architecture, and BST-43 connector pinout. The BMS handshake protocol is identical across the U100i, YARI, and Vulcan variants, so one cell covers the full range without firmware or connector differences.\u003c\/li\u003e\n\n    \u003cli\u003e\n\u003cstrong\u003eBench tested on actual hardware:\u003c\/strong\u003e\n    We cycled this cell on the U100 platform and confirmed the BMS accepted charge without fault flags on first insertion. Charge termination triggered correctly at 4.2V, and the protection circuit tripped cleanly at the low-voltage cutoff threshold during full discharge testing.\u003c\/li\u003e\n\n    \u003cli\u003e\n\u003cstrong\u003eFuel gauge recalibration on first use:\u003c\/strong\u003e\n    After fitting this cell, run one full uninterrupted discharge down to auto-shutdown, then charge to 100% without interruption. The U100's fuel gauge IC maps its percentage readings against this first discharge curve — skipping it leaves the coulomb counter calibrated to the old cell and the percentage display will be inaccurate from day one.\u003c\/li\u003e\n  \u003c\/ul\u003e\n\n  \u003chr class=\"bpw-desc-divider\"\u003e\n\n  \u003ch3 class=\"bpw-desc-h3\"\u003eWhy the U100 reports wrong battery percentage after a BST-43 swap\u003c\/h3\u003e\n\n  \u003cp class=\"bpw-desc-p\"\u003eThe U100 uses a fuel gauge IC that tracks charge state by counting coulombs against a stored discharge curve from the previous cell. When you install a new BST-43, that stored curve no longer matches the new cell's actual voltage-to-capacity profile. The IC keeps using stale reference data until it sees a full uninterrupted cycle. One complete discharge-to-shutdown followed by a full charge resets the reference and brings the percentage display back into line.\u003c\/p\u003e\n\n  \u003ch3 class=\"bpw-desc-h3\"\u003ePhone shuts off suddenly at 20–30% on the replacement cell\u003c\/h3\u003e\n  \u003cp class=\"bpw-desc-p\"\u003eThis happens because the new cell hits a voltage cliff under screen or radio load before the displayed percentage reaches zero. The U100's processor draws a short current spike when the modem transmits or the display backlights — if the cell voltage drops below roughly 3.4V under that load, the phone shuts down even though the resting voltage read by the fuel gauge looked fine a moment earlier. The fix is the same full recalibration cycle: drain completely to auto-shutdown, then charge uninterrupted to 100%. After one full cycle the gauge IC will track the actual voltage curve and the premature cutoff will stop.\u003c\/p\u003e\n\u003c\/div\u003e","brand":"BatteryWeb","offers":[{"title":"Warranty 1 Year","offer_id":43405137969242,"sku":"BWCS-ERX2SL-1","price":23.99,"currency_code":"USD","in_stock":true},{"title":"Warranty 2 Year","offer_id":43405138002010,"sku":"BWCS-ERX2SL-2","price":26.99,"currency_code":"USD","in_stock":true},{"title":"Warranty 3 Year","offer_id":43405138034778,"sku":"BWCS-ERX2SL-3","price":28.99,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0674\/4775\/0746\/files\/BW-CS-ERX2SL-1.webp?v=1779370262","url":"https:\/\/batteryweb.com\/products\/sony-ericsson-u100-replacement-battery-37v-950mah-li-ion","provider":"BatteryWeb","version":"1.0","type":"link"}