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Apple Watch Series 9 A2770 Replacement Battery 3.85V 280mAh

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From $43.99 USD $54.99
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Fits Apple Watch Series 9 models A2770, A2772, A2773, A2857 and one additional variant, replacing OEM part number A2810.
This 3.85V, 280mAh lithium-polymer cell restores full smartwatch runtime on the Series 9 after the original battery degrades from normal charge cycles.
Connector is a two-pin surface-mount pad on the mainboard; orientation is marked with a white dot on the cell housing matching the board silk-screen.
We bench-tested the cell at 3.85V nominal and confirmed the fuel gauge IC accepted the new BMS handshake without fault codes after full charge from disconnect.
After fitting the new cell, place the watch on its magnetic charger immediately and charge to 100% before wearing — the fuel gauge cannot calibrate without a full charge cycle 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

280mAh

Apple Watch Series 9 — 3.85V Li-Polymer Replacement Battery (A2810)

This is a 3.85V, 280mAh Li-Polymer cell (1.08Wh) replacing OEM part A2810 in Apple Watch Series 9. It fits models A2770, A2772, A2773, and A2857. The battery powers the S9 SiP, LTPO display, heart rate sensor array, and Bluetooth/Wi-Fi radios.

  • Series 9 cell compatibility: These four model numbers cover the GPS and GPS + Cellular variants of Series 9 in 41mm and 45mm cases. All share the same A2810 cell footprint, voltage rail, and flex connector — one cell fits across the whole lineup.
  • Bench tested on actual hardware: We ran A2810 cells through charge and discharge cycles on Series 9 hardware. The fuel gauge IC completed calibration cleanly after a full charge cycle from near-zero, and the BMS held stable cutoff voltage without tripping the over-discharge latch.
  • Post-swap charge requirement: After fitting this cell, place the watch on its magnetic charger immediately and charge to 100% before wearing it. The Series 9 fuel gauge IC loses its reference point during cell removal and cannot recalibrate the state-of-charge reading without one full charge cycle from near-zero.

Why the Series 9 fuel gauge reads 0% after a battery swap

The S9 SiP uses a coulomb-counting fuel gauge that tracks charge relative to a stored reference. Removing the old cell wipes that reference entirely. When the new cell lands, the IC has no baseline, so it defaults to 0% or refuses to display a reading. This is not a faulty cell. A single full charge to 100% re-establishes the reference and the percentage will read correctly from that point on.

Watch not pairing to iPhone after battery replacement

Cutting power during a battery swap terminates the active Bluetooth LE session between the watch and iPhone. The watch comes back up without a valid pairing token, so it will not reconnect automatically. On the iPhone, open Settings → Bluetooth, find the watch, tap "Forget This Device," then re-pair through the Watch app. The watch does not need to be reset — only the BLE pairing needs to be re-initiated from the phone side.

Compatible Models

A2770 A2772 A2773 A2857 Watch Series S8 41mm

Replaces Part Numbers

A2810

Technical Specifications

Voltage3.85V
Amp Hours280mAh
Capacity280mAh
Rate1.08Wh
Net Weight6g /0.21 oz
Gross Weight31g /1.09 oz
Approximate Weight31g /1.09 oz
Dimension 26.10 x 20.10 x 4.60mm

Product Highlights

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

Frequently Asked Questions

My Series 9 shows 0% battery and won't turn on right after I put the new cell in — is the battery dead?

The fuel gauge IC loses its charge reference the moment the old cell is disconnected. The new cell is not at fault. Place the watch on the magnetic charger immediately and leave it until it reads 100% — the IC recalibrates during that first full charge cycle and the percentage display returns to normal.

New battery draining completely in less than a day — always-on display was never this bad before

Always-on display combined with continuous heart rate monitoring draws significantly more current against a new cell's slightly different internal impedance than it did against the worn original. This gap narrows over the first five to seven days as the cell settles. If drain persists beyond a week, disable always-on display temporarily via Settings → Display & Brightness and check whether a background app is holding a GPS session open.

Heart rate readings cutting out or going erratic since the battery swap — could the new cell be causing this?

The optical HR sensor array draws pulse current that can cause momentary voltage sag on a new cell before it has completed its first few charge cycles. This is normal for the first week. If the sensor cuts out repeatedly, check that the cell flex connector is fully seated — a partially connected cell will sag harder under sensor load. Press the connector down firmly until it clicks flat against the logic board.

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