{"product_id":"callstel-bfx-300-replacement-battery-37v-900mah-li-ion","title":"Callstel BFX-300 Compatible Battery 3.7V 900mAh Li-ion","description":"\u003cdiv class=\"bpw-desc\"\u003e\n  \u003ch2 class=\"bpw-desc-h2\"\u003eCallstel BFX-300 — 3.7V Li-ion Replacement Battery (TM533443 1S1P)\u003c\/h2\u003e\n\n  \u003cp class=\"bpw-desc-lead\"\u003eThis 3.7V, 900mAh Li-ion cell replaces the original battery in the Callstel BFX-300 portable car speaker. The TM533443 1S1P matches the factory cell's footprint at 46.20 × 34.14 × 5.68mm. When the BFX-300 no longer powers on or drops off early under load, this is the direct swap.\u003c\/p\u003e\n\n  \u003cul class=\"bpw-desc-bullets\"\u003e\n    \u003cli\u003e\n\u003cstrong\u003eBFX-300 fit:\u003c\/strong\u003e\n    The BFX-300 runs a single-cell 3.7V architecture — one cell, one protection circuit. Any cell going into this speaker must match that 1S1P configuration. A mismatched cell trips the onboard BMS at startup and the speaker will not initialise.\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 a BFX-300 unit, monitoring BMS handshake and cutoff behaviour. The protection circuit engaged correctly at low-voltage threshold and accepted charge from the factory USB input without fault.\u003c\/li\u003e\n\n    \u003cli\u003e\n\u003cstrong\u003eFirst-cycle volume control:\u003c\/strong\u003e\n    Run the BFX-300 at no more than 60% volume during the first full charge cycle. High-volume bass draws peak current before the new cell is conditioned, and the BMS can trigger early protection cutoff — leaving the speaker appearing dead before the cell is even warm.\u003c\/li\u003e\n  \u003c\/ul\u003e\n\n  \u003chr class=\"bpw-desc-divider\"\u003e\n\n  \u003ch3 class=\"bpw-desc-h3\"\u003eWhy the BFX-300 loses bass depth at high volume on a fresh battery\u003c\/h3\u003e\n\n  \u003cp class=\"bpw-desc-p\"\u003eSub-bass frequencies demand short, sharp current spikes from the cell. A 900mAh 1S1P cell has a finite discharge rate, and at high volume those spikes pull the cell voltage below the amplifier's stable operating window. The result is audible bass rolloff — not a speaker fault, but a voltage sag event. This is most noticeable on tracks with sustained low-frequency content. Keeping volume under 75% on a new cell reduces sag until the cell has completed a few full cycles.\u003c\/p\u003e\n\n  \u003ch3 class=\"bpw-desc-h3\"\u003eBFX-300 speaker cuts out completely before the battery indicator shows low\u003c\/h3\u003e\n  \u003cp class=\"bpw-desc-p\"\u003eThe BMS protection circuit responds to instantaneous voltage drop, not average charge level. At high amplifier draw, the cell can dip below the BMS cutoff threshold — around 2.75V — even when the displayed charge reads mid-level. The speaker shuts off abruptly as protection trips. To recover, disconnect the USB charge cable, wait 10 seconds, and reconnect — this resets the BMS and allows the cell voltage to recover before restart.\u003c\/p\u003e\n\u003c\/div\u003e","brand":"BatteryWeb","offers":[{"title":"Warranty 1 Year","offer_id":43339814862938,"sku":"BWCS-BTK112FR-1","price":23.99,"currency_code":"USD","in_stock":true},{"title":"Warranty 2 Year","offer_id":43339814895706,"sku":"BWCS-BTK112FR-2","price":26.99,"currency_code":"USD","in_stock":true},{"title":"Warranty 3 Year","offer_id":43339814928474,"sku":"BWCS-BTK112FR-3","price":28.99,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0674\/4775\/0746\/files\/BW-CS-BTK112FR-1.webp?v=1778366788","url":"https:\/\/batteryweb.com\/products\/callstel-bfx-300-replacement-battery-37v-900mah-li-ion","provider":"BatteryWeb","version":"1.0","type":"link"}