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JBL SD-18 Compatible Battery 3.7V 1000mAh Li-Polymer SP603048

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From $33.99 USD $41.99
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Fits JBL SD-18 and SD-21 portable speakers; replaces OEM part SP603048.
3.7V, 1000mAh Li-Polymer cell delivers rated capacity for full audio playback cycles.
Connector slides into existing battery slot with locking tab; orientation marked on housing.
Bench tested on SD-18 — BMS accepted charge cycle without fault codes; discharge curve stable.
On first insertion, power the speaker fully off, wait ten seconds, then power on to sync fuel gauge with new cell capacity.
Extended delivery time

Available by SPECIAL ORDER. Delivery for this product typically takes 2 weeks.

Extra Discount: As a thank you for your patience, enjoy an extra 5% off your order
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Battery Care Tips

🔹 Getting Started

Charge your new battery fully before you use it for the first time. Over the next few charge cycles, run your device down to around 20% before you recharge—this helps the battery perform its best. After that, charge whenever you need to.

🔹 Keep It Healthy

Avoid letting your battery completely drain or staying plugged in constantly. Both extremes wear it out faster. Store the battery in a cool, dry place when you're not using it, since heat damages batteries quickly.

Delivery and Shipping

🔹 Most orders ship the next day, and we use FedEx, UPS, Purolator and other carriers to get them to you. Lithium batteries have to ship by ground only, not air or USPS. Make sure your address is right before you order, because if we have to send it back, you pay for shipping again.

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⚠️ Disclaimer: All product names, trademarks, and registered trademarks belong to their respective owners.

🔹 We use these names, brands, or model numbers only for identification and compatibility purposes.

Voltage

3.7V

Amp

1000mAh

JBL SD-18 / SD-21 — 3.7V Li-Polymer Replacement Battery (SP603048)

This 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.

  • SD-18 and SD-21 compatibility: 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.
  • Bench tested on actual hardware: 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.
  • Fuel gauge calibration after install: 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.

Why the SD-18 cuts audio abruptly at moderate volume on a new battery

At 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.

Battery indicator reads 50% then speaker shuts off without warning

This 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.

Compatible Models

SD-18 SD-21

Replaces Part Numbers

SP603048

Technical Specifications

Voltage3.7V
Amp Hours1000mAh
Capacity1000mAh
Rate3.7Wh
Net Weight18g /0.63 oz
Gross Weight43g /1.52 oz
Approximate Weight43g /1.52 oz
Dimension 50.40 x 29.80 x 18.00mm

Product Highlights

  • Brand: JBL
  • Manufacturer: CS
  • Series: Standard
  • Color: Black
  • Product Type: Li-Polymer
  • Battery Type: Li-Polymer
  • Warranty: 12 Months
  • Bulk Orders: sales@batteryweb.com

Frequently Asked Questions

My JBL SD-18 shows a full charge bar but the audio drops out after about an hour of play — is that the battery?

Yes. This is fuel gauge drift — the indicator is reading off a stale baseline that no longer matches the new or degraded cell's actual capacity. The speaker hits true low voltage well before the display says so, and the BMS shuts audio output to protect the cell. Run the speaker down until it powers off on its own, then charge it fully without interruption. After that single full cycle the gauge re-anchors and the dropout point aligns with what the indicator shows.

Bluetooth keeps cutting out when I push the SD-18 to high volume, but it stays connected at low volume — what's happening?

At high volume the amplifier draws current spikes that the Bluetooth radio then has to compete with. If the cell has any elevated internal resistance — common after storage or with an aged battery — combined amp-plus-radio draw causes a voltage sag. The radio module loses its minimum operating voltage and drops the connection even though the amp keeps running. Fitting a fresh SP603048 cell and running one full charge cycle reduces internal resistance enough that both the amp and radio stay above their floor voltages simultaneously.

The SD-21 speaker feels warm through the fabric housing after an hour of play — is that normal or is the battery overheating?

Some warmth is expected — the amplifier generates heat during playback and the battery adds discharge heat inside a sealed fabric enclosure. What's not normal is the housing becoming hot to the touch or the speaker shutting down mid-song due to thermal cutoff. If you're seeing either of those, check that the vents on the unit are unobstructed and avoid placing the speaker on soft surfaces like a couch cushion that blocks airflow. Sustained temperatures that trigger shutdown indicate the original battery's internal resistance has risen — at that point the SP603048 replacement cell will reduce heat output at the source.

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