{"product_id":"boostmobile-legacy-replacement-battery-385v-3900mah-li-polymer","title":"BoostMobile Legacy CPLD-428 Compatible Battery 3.85V 3900mAh","description":"\u003cdiv class=\"bpw-desc\"\u003e\n  \u003ch2 class=\"bpw-desc-h2\"\u003eBoostMobile Legacy \/ CP3705AS — 3.85V Li-Polymer Replacement Battery (CPLD-428)\u003c\/h2\u003e\n\n  \u003cp class=\"bpw-desc-lead\"\u003eThis is a 3900mAh Li-Polymer cell at 3.85V nominal, built to the CPLD-428 specification. It fits the BoostMobile Legacy and CP3705AS smartphones directly. If the original cell is swelling, no longer holding a charge, or causing unexpected shutdowns, this is the correct replacement.\u003c\/p\u003e\n\n  \u003cul class=\"bpw-desc-bullets\"\u003e\n    \u003cli\u003e\n\u003cstrong\u003eLegacy and CP3705AS compatibility:\u003c\/strong\u003e\n    Both models share the same battery bay dimensions, connector pinout, and BMS handshake protocol — the CPLD-428 spec covers both. The cell footprint is 88.24 × 66.30 × 4.25mm, so fit is exact with no case modification.\u003c\/li\u003e\n\n    \u003cli\u003e\n\u003cstrong\u003eBench tested on actual hardware:\u003c\/strong\u003e\n    We ran this cell through charge and discharge cycles on the Legacy platform. The BMS accepted the new cell without triggering a fault code, and the charge IC stepped through trickle, CC, and CV phases correctly at each stage.\u003c\/li\u003e\n\n    \u003cli\u003e\n\u003cstrong\u003eFuel gauge recalibration on first use:\u003c\/strong\u003e\n    On first use after installation, disable fast charging and run one full discharge-to-charge cycle. This lets the fuel gauge IC map its coulomb counter against the new cell's discharge curve before high-current charging pushes current into an uncalibrated register.\u003c\/li\u003e\n  \u003c\/ul\u003e\n\n  \u003chr class=\"bpw-desc-divider\"\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 problem, not a capacity problem. Under modem transmission load or peak screen brightness, the new cell briefly drops below the BMS cutoff threshold — even though the OS reports 20–30% remaining. The fuel gauge IC is still calibrated to the old, degraded cell's curve, so reported percentage and actual cell voltage are mismatched. Run one complete discharge cycle down to automatic shutdown, then charge uninterrupted to 100%. After that cycle, the coulomb counter recalibrates and shutdowns at low percentage typically stop.\u003c\/p\u003e\n\n  \u003ch3 class=\"bpw-desc-h3\"\u003eOS reporting wrong battery percentage after cell swap\u003c\/h3\u003e\n  \u003cp class=\"bpw-desc-p\"\u003eThe Legacy's fuel gauge IC stores a learned discharge curve from the old cell. Swapping the physical cell does not reset this stored curve — the IC continues to calculate percentage against data that no longer matches the new cell's chemistry. You will see the percentage jump erratically or read high while the phone shuts down under load. The fix is one complete uninterrupted discharge to zero, followed by a full charge to 100% with fast charging disabled — this forces the IC to rewrite its learned curve against the new cell.\u003c\/p\u003e\n\u003c\/div\u003e","brand":"BatteryWeb","offers":[{"title":"Warranty 1 Year","offer_id":43391990923354,"sku":"BWCS-CPL370SL-1","price":26.99,"currency_code":"USD","in_stock":true},{"title":"Warranty 2 Year","offer_id":43391990956122,"sku":"BWCS-CPL370SL-2","price":29.99,"currency_code":"USD","in_stock":true},{"title":"Warranty 3 Year","offer_id":43391990988890,"sku":"BWCS-CPL370SL-3","price":32.99,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0674\/4775\/0746\/files\/BW-CS-CPL370SL-1.webp?v=1779142762","url":"https:\/\/batteryweb.com\/products\/boostmobile-legacy-replacement-battery-385v-3900mah-li-polymer","provider":"BatteryWeb","version":"1.0","type":"link"}