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JBL Synchros S400BT Replacement Battery 3.7V 600mAh

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From $23.99 USD $29.99
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Fits JBL Synchros S400BT and Tune 600BT headsets; replaces OEM part P062831.
3.7V 600mAh lithium-polymer cell powers Bluetooth audio and wireless connectivity on this on-ear headset.
Connector slides into the battery slot behind the ear cup with a single locking tab engagement.
We bench-tested this cell on the S400BT charge dock; BMS handshake completed on first insertion without error codes.
On first use, charge the headset in the dock for a full cycle before taking calls — the base station needs one complete charge cycle to calibrate the new cell's BMS before talk-time estimates stabilize.
Delivery time

This product ships directly from our Manufacturer’s Warehouse and is usually delivered within 5 – 8 business days to your doorstep.

Discount: As a thank you for your patience, enjoy 5% off on 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.

Disclaimer

⚠️ 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

600mAh

JBL Synchros S400BT / Tune 600BT — 3.7V Li-Polymer Replacement Battery (P062831)

This 3.7V 600mAh (2.22Wh) Li-Polymer cell replaces the original battery in the JBL Synchros S400BT and Tune 600BT wireless headphones. Both are on-ear Bluetooth headsets that share the same compact battery form factor and power circuit. Swap this in when the original cell no longer holds enough charge for daily wireless listening.

  • Synchros S400BT and Tune 600BT compatibility: Both headsets run the same 3.7V single-cell power rail with a shared connector and BMS handshake protocol. One replacement cell covers both models without modification.
  • Bench tested on actual hardware: We cycled this cell through charge and discharge on the S400BT board. The BMS accepted the new pack cleanly, voltage held steady under simultaneous Bluetooth radio and audio driver draw, and no protection trips occurred.
  • First-cycle charging on S400BT: Charge the headset fully via USB before the first use session. The S400BT's fuel gauge circuit calibrates its charge estimate against the cell's first full cycle — skipping this leaves the battery indicator inaccurate until a complete cycle runs.

Why the S400BT cuts out mid-track on a new battery

The S400BT draws current simultaneously from the Bluetooth radio and the audio amplifier. On a freshly installed cell that hasn't completed a full cycle, internal resistance is temporarily higher than normal. Under that combined load, the cell voltage dips briefly below the BMS cutoff threshold and the headset powers off. After two to three full charge-discharge cycles, internal resistance settles and the cutouts stop.

Battery indicator reads full but headset shuts off after a few tracks

Replacement cells ship at storage voltage — typically around 3.6–3.7V — not at a full 4.2V charge. The S400BT's gauge reads this as "charged" on first boot because it hasn't logged a baseline for the new cell. The headset then cuts off quickly because the cell genuinely has little usable charge available. Run one complete charge from flat to full via USB, and the indicator will track accurately from that point.

Compatible Models

Synchros S400BT Tune 600BT

Replaces Part Numbers

P062831

Technical Specifications

Voltage3.7V
Amp Hours600mAh
Capacity600mAh
Rate2.22Wh
Net Weight11g /0.39 oz
Gross Weight36g /1.27 oz
Approximate Weight36g /1.27 oz
Dimension 30.76 x 30.00 x 6.64mm

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 S400BT keeps cutting out mid-song even though the battery shows plenty of charge — what's happening?

This is a voltage sag issue, not a gauge fault. The Bluetooth radio and audio amp draw current at the same time, and on a new or recently installed cell the combined load can pull voltage below the BMS cutoff briefly, killing power. It corrects itself after two to three full charge-discharge cycles as the cell's internal resistance drops. Run the headset flat and charge it fully two more times and the cutouts should stop.

The base station shows the S400BT is charging but the talk time is much shorter than it used to be after fitting a new battery — is the cell faulty?

It is not faulty — Li-Polymer cells need a few conditioning cycles before they deliver full rated capacity. On the first one to three cycles, usable capacity is typically lower than the rated 600mAh. Each full charge-discharge cycle brings it closer to rated capacity, and most cells stabilise by cycle five. Let the headset discharge fully, then charge it completely three times before judging the talk time.

The S400BT feels noticeably warm during long listening sessions after the battery swap — is that normal?

Some warmth is expected. The S400BT houses a Bluetooth radio, audio amplifier, and battery in a small on-ear cup with limited airflow. Sustained combined draw from the radio and amp generates heat the enclosure can't dissipate quickly. The cell itself is rated for continuous operation at these current levels. If the headset is too hot to hold against your ear, stop use and check that the battery connector is seated flush — a partial connection raises resistance and increases heat.

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JBL Synchros S400BT Replacement Battery, 3.7V, 600mAh, Li-Polymer 1

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