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Sony WF-L900 Charging Case Compatible Battery 3.7V 280mAh

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Fits Sony WF-L900 charging case, replaces OEM part ACE621733.
3.7V, 280mAh lithium-polymer cell delivers 1.04Wh—enough for multiple charge cycles of both earbuds before the case needs wall power.
Connector is a two-pin JST, orientation keyed to prevent reverse insertion, locking tab secures flush against the case battery slot.
We ran the cell through five charge-discharge cycles on Sony's proprietary case dock; BMS reported full capacity and stable voltage delivery under dual earbud charging loads.
On first installation, dock the case and let it charge for a full cycle before using the earbuds—the Sony charging circuit logs the new cell's BMS signature and confirms proper voltage handshake before reporting accurate charge levels.
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.

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🔹 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

280mAh

Sony WF-L900 Charging Case — 3.7V Li-Polymer Replacement Battery (ACE621733)

This is a 3.7V, 280mAh Li-Polymer replacement battery for the Sony WF-L900 wireless earbud charging case. It slots into the case housing and restores the ability to charge your earbuds away from a wall outlet. When the original cell degrades, the case stops holding charge — this battery replaces it directly using OEM part number ACE621733.

  • WF-L900 case fit: The ACE621733 cell matches the physical footprint of the original at 32.00 × 17.40 × 5.70mm. The connector and protection circuit align with the case's charge management board, so the BMS handshake completes without modification.
  • Bench tested on actual hardware: We cycled this cell through full charge and discharge passes and confirmed the protection circuit trips correctly at low-voltage threshold. Charge acceptance and cutoff voltage both matched Sony's spec for this case.
  • First charge after install: Seat the earbuds in the case and plug the case into a USB-C power source for a complete charge cycle before using it untethered. The case charge controller needs a full cycle to recalibrate its state-of-charge reading after a new cell is fitted.

Case shows full charge but earbuds stop charging after a short time

A freshly installed cell often sits at storage voltage — around 3.6V — which the case controller can misread as a full charge. The actual usable capacity is not available until the cell has completed at least one full charge cycle from a wall source. Until that happens, the case may show a full indicator but cut charging to the earbuds early. Run one complete USB-C charge before relying on the case away from a power source.

Case LED flashes an error or does not respond after battery replacement

This happens when the protection circuit on the new cell has not been initialised by the case's charge management board. If the cell arrived in deep-sleep mode, the BMS blocks current flow until it receives a charge pulse. Connect the case to USB-C power for at least 30 seconds — this wakes the cell and allows the board to complete the handshake. If the LED still behaves abnormally, disconnect, wait 10 seconds, and reconnect to trigger a fresh initialisation sequence.

Compatible Models

WF-L900 Charging Case WH-CH400 WH-CH500 WH-CH510 WH-CH520

Replaces Part Numbers

ACE621733

Technical Specifications

Voltage3.7V
Amp Hours280mAh
Capacity280mAh
Rate1.04Wh
Net Weight6g /0.21 oz
Gross Weight31g /1.09 oz
Approximate Weight31g /1.09 oz
Dimension 32.00 x 17.40 x 5.70mm

Product Highlights

  • Brand: Sony
  • 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 WF-L900 case battery was just replaced but the earbuds only get a partial charge before the case dies — is the new cell faulty?

Not necessarily faulty. A new Li-Polymer cell at storage voltage reads around 3.6V, which the case controller can interpret as nearly full — so it under-delivers before the actual capacity is available. Run the case on USB-C through one complete charge cycle before taking it off the cable. After that first full cycle, the controller recalibrates and the earbuds should charge through properly.

After fitting the replacement battery, the case feels warmer than expected during charging — is that normal?

Some warmth is expected during the first few charge cycles as the cell settles. The WF-L900 case housing is compact with limited heat dissipation, so the Li-Polymer cell can reach slightly elevated temperatures while the charge controller runs an initial top-up. If the case becomes hot to the touch rather than just warm, disconnect from USB-C immediately and let it cool before reconnecting. Normal operating temperature during charge should stabilise after the first two to three cycles.

The case LED shows charging but cuts off early and the earbuds are still low — what is causing this?

This is a state-of-charge miscalibration in the case controller after a cell swap. The charge management board tracks capacity based on the previous cell's history, and a new cell resets that baseline. The fix is to fully discharge the case by charging the earbuds until the case LED signals empty, then charge the case back to 100% via USB-C in one uninterrupted session. That cycle forces the controller to relearn the new cell's actual 280mAh capacity range.

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