{"product_id":"jbl-sd-18-replacement-battery-37v-1000mah-li-polymer","title":"JBL SD-18 Compatible Battery 3.7V 1000mAh Li-Polymer SP603048","description":"\u003cdiv class=\"bpw-desc\"\u003e\n  \u003ch2 class=\"bpw-desc-h2\"\u003eJBL SD-18 \/ SD-21 — 3.7V Li-Polymer Replacement Battery (SP603048)\u003c\/h2\u003e\n\n  \u003cp class=\"bpw-desc-lead\"\u003eThis is a 3.7V, 1000mAh Li-Polymer battery for the JBL SD-18 and SD-21 portable speakers. It matches the OEM part number SP603048 and fits the original cell housing. Swap it in when the original battery no longer holds a charge or won't power the speaker at all.\u003c\/p\u003e\n\n  \u003cul class=\"bpw-desc-bullets\"\u003e\n    \u003cli\u003e\n\u003cstrong\u003eSD-18 and SD-21 compatibility:\u003c\/strong\u003e\n    Both models run the same 3.7V single-cell architecture with identical connector pinout and BMS handshake. One battery covers both units — no firmware or hardware difference affects the fitment.\u003c\/li\u003e\n\n    \u003cli\u003e\n\u003cstrong\u003eBench tested on actual hardware:\u003c\/strong\u003e\n    We ran the SP603048 cell through charge cycles on the SD-18 board. The BMS accepted the cell cleanly at first connect, balanced charge current correctly, and tripped the low-voltage cutoff at the expected threshold without false shutdowns.\u003c\/li\u003e\n\n    \u003cli\u003e\n\u003cstrong\u003eFuel gauge calibration after install:\u003c\/strong\u003e\n    After fitting a new cell, run the speaker down until it shuts off on its own, then charge it uninterrupted to 100%. This lets the onboard fuel gauge recalibrate to the new cell's actual capacity — skipping this step causes the battery indicator to read inaccurately 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 SD-18 cuts audio abruptly at moderate volume on a new battery\u003c\/h3\u003e\n  \u003cp class=\"bpw-desc-p\"\u003eAt higher playback levels, the amplifier draws current in short, sharp spikes. A Li-Polymer cell that has been stored for a long time can have elevated internal resistance even at full charge. That resistance causes a voltage sag under the amp's peak draw, and the BMS interprets the sag as a low-cell event and cuts output. Leaving the replacement battery on a full charge cycle for several hours before first use lowers internal resistance enough that the BMS stops tripping on amp transients.\u003c\/p\u003e\n\n  \u003ch3 class=\"bpw-desc-h3\"\u003eBattery indicator reads 50% then speaker shuts off without warning\u003c\/h3\u003e\n  \u003cp class=\"bpw-desc-p\"\u003eThis happens when the fuel gauge loses sync with the cell — usually because the original battery degraded gradually and the gauge was never reset. The indicator reflects an old capacity baseline, not the new cell's state. The fix is a full discharge-to-cutoff followed by a full uninterrupted charge. After one complete cycle the gauge re-anchors to the replacement cell and the reported percentage tracks actual charge accurately again.\u003c\/p\u003e\n\u003c\/div\u003e","brand":"BatteryWeb","offers":[{"title":"Warranty 1 Year","offer_id":43416194777178,"sku":"BWCS-JBD180SL-1","price":33.99,"currency_code":"USD","in_stock":true},{"title":"Warranty 2 Year","offer_id":43416194809946,"sku":"BWCS-JBD180SL-2","price":39.99,"currency_code":"USD","in_stock":true},{"title":"Warranty 3 Year","offer_id":43416194842714,"sku":"BWCS-JBD180SL-3","price":43.99,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0674\/4775\/0746\/files\/BW-CS-JBD180SL-1.webp?v=1779760768","url":"https:\/\/batteryweb.com\/products\/jbl-sd-18-replacement-battery-37v-1000mah-li-polymer","provider":"BatteryWeb","version":"1.0","type":"link"}