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Huawei Watch 3 Pro Compatible Battery HB642735ECW 3.85V 660mAh

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From $38.99 USD $47.99
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Replaces HB642735ECW battery for Huawei Watch 3 Pro, Watch 3S, and Watch 3X smartwatches.
This 3.85V, 660mAh lithium-polymer cell restores multi-day runtime for fitness tracking, GPS navigation, and heart rate monitoring.
Connector seats flush into the watch housing with a single contact pad; alignment matters on reassembly.
We ran the cell through full charge cycles on a Watch 3 Pro test unit; the BMS initialized cleanly without fault codes.
After fitting this cell, place the watch on its magnetic charger immediately and charge to 100% — the fuel gauge IC cannot calibrate without a complete charge from near-zero after a swap.
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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

3.85V

Amp

660mAh

Huawei Watch 3 Pro / Watch 3S / Watch 3X — 3.85V Li-Polymer Replacement Battery (HB642735ECW)

This 3.85V, 660mAh Li-Polymer cell replaces the OEM battery in the Huawei Watch 3 Pro, Watch 3S, and Watch 3X smartwatches. It fits the original battery bay and connector without modification. Physical dimensions are 32.80 × 25.70 × 6.30mm — measure your existing cell before ordering if you are unsure.

  • Watch 3 Pro, 3S, and 3X compatibility: All three models share the HB642735ECW cell format, the same connector pinout, and an identical fuel gauge IC interface. The BMS handshake is consistent across the series, so one cell covers all three variants.
  • Bench tested on actual hardware: We ran this cell through charge and discharge cycles on a Watch 3 Pro unit. The fuel gauge IC accepted the new cell, BMS protection tripped correctly at low-voltage cutoff, and charge termination behaved normally at full capacity.
  • Fuel gauge calibration after swap: Place the watch on its magnetic charger immediately after fitting this cell and charge it to 100% before first use. The fuel gauge IC on this platform loses its reference point when the cell is removed — it cannot report accurate state-of-charge until it completes one full charge cycle from near-zero.

Why always-on display and continuous HR monitoring drain this cell faster than expected

The Watch 3 Pro draws current from three simultaneous sources when AOD and heart rate monitoring run together: the AMOLED panel, the optical HR sensor, and the GPS receiver during workouts. A new cell at a different impedance than the aged original will show a different discharge curve for the first several cycles. Current draw from the HR sensor is higher on a fresh cell because the sensor auto-adjusts gain against the new impedance profile. This normalises within five to seven charge cycles.

Watch not pairing with phone after battery replacement

Removing the battery clears the active BLE session between the watch and the Huawei Health app. The watch does not automatically re-establish a paired connection after power is restored — it waits for the host device to initiate. On your phone, open Huawei Health, go to the device settings for the watch, tap "Forget device," then re-add it from scratch. This resets the BLE handshake and resolves the pairing failure without a factory reset of the watch itself.

Compatible Models

Watch 3 Pro Watch 3S Watch 3X

Replaces Part Numbers

HB642735ECW

Technical Specifications

Voltage3.85V
Amp Hours660mAh
Capacity660mAh
Rate2.54Wh
Net Weight11g /0.39 oz
Gross Weight36g /1.27 oz
Approximate Weight36g /1.27 oz
Dimension 32.80 x 25.70 x 6.30mm

Product Highlights

  • Brand: Huawei
  • 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 Huawei Watch 3 Pro shows 0% and won't turn on right after I swapped the battery — did I get a dead cell?

The cell is almost certainly fine. The fuel gauge IC on the Watch 3 series loses its charge reference when the original cell is disconnected, so it reads 0% by default after a swap. Place the watch on its magnetic charger immediately and leave it until it reaches 100% — do not try to power it on mid-charge. After one full charge cycle from near-zero, the IC recalibrates and the percentage display returns to normal.

The battery I just fitted is draining in about a day — my old one used to last two or three days. What's wrong?

A new cell at a different impedance than the degraded original causes the HR sensor to run at higher gain while it adjusts to the new power source. This elevated draw is normal for the first week and settles after five to seven full charge cycles. Check that always-on display is not enabled and that continuous heart rate monitoring is set to intervals rather than constant — those two settings together are the largest current draw on this platform. If drain remains excessive after ten cycles, check Huawei Health for any third-party watchfaces or apps polling the GPS in the background.

The magnetic charger isn't making contact properly after I reassembled the watch — the charging screen never appears.

This is almost always a seating issue with the rear cover after reassembly. The magnetic charging contacts on the Watch 3 Pro sit flush against pads on the rear case — if the cover is even slightly raised or rotated, the magnet aligns but the contacts miss. Remove the rear cover, reseat it firmly, and ensure the alignment notches click. Then place the charger dead-centre on the rear and confirm the charging indicator appears within ten seconds. If contact is still intermittent, clean both the watch contacts and charger pins with a dry cotton swab before reseating.

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