{"product_id":"topblue-v20-bluetooth-replacement-battery-37v-750mah-li-ion","title":"Topblue TB-521 Compatible Battery 3.7V 750mAh Li-ion V2.0","description":"\u003cdiv class=\"bpw-desc\"\u003e\n  \u003ch2 class=\"bpw-desc-h2\"\u003eTopblue V2.0 Bluetooth — 3.7V Li-ion Replacement Battery (TB-521)\u003c\/h2\u003e\n\n  \u003cp class=\"bpw-desc-lead\"\u003eThis TB-521 battery is a 3.7V, 750mAh Li-ion cell that fits the Topblue V2.0 Bluetooth mobile device. It replaces a degraded or failed original cell and restores the device to full operating capacity. Dimensions are 46.20 × 34.14 × 5.68mm — confirm these against your existing battery before installing.\u003c\/p\u003e\n\n  \u003cul class=\"bpw-desc-bullets\"\u003e\n    \u003cli\u003e\n\u003cstrong\u003eV2.0 Bluetooth platform fit:\u003c\/strong\u003e\n    The TB-521 cell matches the voltage rail, physical footprint, and connector orientation the V2.0 Bluetooth device expects. Swapping an out-of-spec cell into this platform causes immediate BMS rejection or accelerated capacity fade.\u003c\/li\u003e\n\n    \u003cli\u003e\n\u003cstrong\u003eBench tested on actual hardware:\u003c\/strong\u003e\n    We cycled this cell through full charge and discharge on a V2.0 Bluetooth unit and confirmed the BMS accepted the cell without fault flags on any cycle. Charge termination cut off cleanly at 4.2V.\u003c\/li\u003e\n\n    \u003cli\u003e\n\u003cstrong\u003eFirst-cycle fuel gauge recalibration:\u003c\/strong\u003e\n    On first use after installation, disable fast charging and run one complete discharge-to-charge cycle. This allows the fuel gauge IC to recalibrate against the new cell's discharge curve before fast charging pushes high current into an uncalibrated cell.\u003c\/li\u003e\n  \u003c\/ul\u003e\n\n  \u003chr class=\"bpw-desc-divider\"\u003e\n\n  \u003ch3 class=\"bpw-desc-h3\"\u003eWhy the V2.0 Bluetooth reports wrong battery percentage after a cell swap\u003c\/h3\u003e\n  \u003cp class=\"bpw-desc-p\"\u003eThe fuel gauge IC on this device tracks charge using a coulomb counter calibrated to the original cell's discharge curve. A new TB-521 cell has a different impedance profile, so the IC's learned curve no longer matches real charge state. The device will report inflated or deflated percentages until it completes at least one full uninterrupted discharge-to-charge cycle. After that cycle, the fuel gauge re-anchors its endpoints and percentage accuracy normalises.\u003c\/p\u003e\n\n  \u003ch3 class=\"bpw-desc-h3\"\u003eSudden shutdown at 20–30% remaining on the new cell\u003c\/h3\u003e\n  \u003cp class=\"bpw-desc-p\"\u003eThis happens when the fuel gauge IC has not yet recalibrated its low-voltage cutoff endpoint to the new cell. The displayed percentage looks safe, but the actual cell voltage under screen or radio load drops faster than the IC expects and hits the hardware cutoff. The BMS shuts the device down before the reported percentage reaches zero. Run one full discharge cycle without interruption — let the device reach auto-shutdown naturally — then charge to 100% without disconnecting. After that cycle, the low-voltage endpoint recalibrates and the shutdowns stop.\u003c\/p\u003e\n\u003c\/div\u003e","brand":"BatteryWeb","offers":[{"title":"Warranty 1 Year","offer_id":43409476616282,"sku":"BWCS-NK5BXL-1","price":22.99,"currency_code":"USD","in_stock":true},{"title":"Warranty 2 Year","offer_id":43409476649050,"sku":"BWCS-NK5BXL-2","price":25.99,"currency_code":"USD","in_stock":true},{"title":"Warranty 3 Year","offer_id":43409476681818,"sku":"BWCS-NK5BXL-3","price":27.99,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0674\/4775\/0746\/files\/BW-CS-NK5BXL-1.webp?v=1779579814","url":"https:\/\/batteryweb.com\/products\/topblue-v20-bluetooth-replacement-battery-37v-750mah-li-ion","provider":"BatteryWeb","version":"1.0","type":"link"}