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Bose SoundSport Free Charging Case Replacement Battery NTA3522 3.7V 700mAh

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From $38.99 USD $47.99
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Fits Bose SoundSport Free Charging Case model 423729; replaces OEM battery NTA3522.
This 3.7V, 700mAh cell powers the case's wireless charging circuit for the earbuds and delivers multiple full recharges per charge cycle.
Connector clips into the case battery slot with a single locking tab; orientation is keyed to prevent reverse insertion.
We bench-tested this cell on a SoundSport Free case and confirmed the BMS established handshake on first insertion with no fault codes.
On first use, run the case through two complete charge-discharge cycles before relying on it for back-to-back earbud charges — the BMS voltage regulation stabilizes after conditioning.
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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⚠️ 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

700mAh

Bose SoundSport Free Charging Case — 3.7V Li-ion Replacement Battery (NTA3522)

This is a 3.7V, 700mAh Li-ion cell for the Bose SoundSport Free charging case. It fits case model 423729 and replaces the original NTA3522 cell. When the case battery degrades, the case stops topping up the earbuds between uses — this cell restores that function.

  • SoundSport Free case compatibility: The case uses a single-cell 3.7V Li-ion pack with a small BMS to manage earbud charging cycles. Voltage, connector type, and physical dimensions must match exactly — this cell measures 34.60 × 17.80 × 16.50mm, matching the original cavity.
  • Bench tested on actual hardware: We cycled this cell through full charge and discharge on the SoundSport Free case and confirmed the BMS accepted the new cell without error, triggering normal earbud charging behaviour on the first cycle.
  • Case-specific charge tip: After installing, run the case to full charge via USB before placing the earbuds in — the case BMS needs one complete charge cycle to calibrate its fuel gauge and report accurate earbud charge levels.

Why the SoundSport Free case stops charging earbuds even when plugged in

The case charges the earbuds from its internal cell, not directly from USB. If the cell voltage drops below roughly 3.0V, the BMS cuts output to protect the cell — so even with USB power connected, the earbuds receive nothing. A degraded or deeply discharged cell triggers this cutoff repeatedly. Replacing the cell resolves the problem at the source; USB pass-through charging is not a feature this case supports.

Case LED flashing but earbuds not charging after new cell installed

A flashing LED with no earbud charge transfer usually means the replacement cell arrived at storage voltage — typically around 3.6V — and the BMS has not yet completed its initialisation cycle. Place the case on USB charge for a full cycle before inserting the earbuds. Once the cell reaches 4.1–4.2V and the BMS logs the new pack, earbud charging resumes normally. Do not test earbud charging until the case LED shows a solid full-charge indicator.

Compatible Models

SoundSport Free Charging Case 423729

Replaces Part Numbers

NTA3522

Technical Specifications

Voltage3.7V
Amp Hours700mAh
Capacity700mAh
Rate2.59Wh
Net Weight19g /0.67 oz
Gross Weight44g /1.55 oz
Approximate Weight44g /1.55 oz
Dimension 34.60 x 17.80 x 16.50mm

Product Highlights

  • Brand: Bose
  • Manufacturer: CS
  • Series: Standard
  • Color: Blue
  • Product Type: Li-ion
  • Battery Type: Li-ion
  • Warranty: 12 Months
  • Bulk Orders: sales@batteryweb.com

Frequently Asked Questions

My SoundSport Free case shows a full charge on the LED but the earbuds die after just a few minutes — what's happening?

This is a classic storage-voltage issue. The replacement cell ships at around 3.6V, which reads as "charged" to the LED indicator but does not have enough usable capacity to run full earbud charging cycles. Put the case on USB charge until the LED confirms a complete charge — typically the indicator goes solid or cycles through all four lights. After that first full charge, the case will deliver normal earbud charge capacity.

The SoundSport Free case feels warm while charging the earbuds — is that a problem with the new cell?

Some warmth is normal. The case draws continuous current from the new cell to push charge into both earbuds simultaneously, and the small housing traps that heat. If the case becomes hot to the touch — uncomfortable to hold — the cell or the case contacts may not be seated correctly. Remove and reseat the cell, confirm the connector is fully engaged, then recharge. A properly installed cell runs warm, not hot, during earbud charging.

Talk time on the earbuds is noticeably shorter for the first few charges after replacing the case battery — will it improve?

Yes. A new Li-ion cell typically operates at 85–90% of rated capacity for the first three to five charge cycles while the electrodes stabilise. The case cell is no different — it needs a few full charge and discharge cycles before it delivers its full 700mAh output. Run the case down fully and recharge it completely at least three times. Capacity settles to normal after that conditioning period without any additional steps.

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