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Samsung Galaxy Watch3 45mm Replacement Battery 3.85V 330mAh

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From $24.99 USD $30.99
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Fits Samsung Galaxy Watch3 45mm; replaces OEM part EB-BR840ABY and GH43-05011A.
This 3.85V, 330mAh lithium-polymer cell restores full runtime on fitness tracking, heart rate monitoring, and GPS functions.
Connector seats flat into the watch housing with magnetic charger alignment pins; no locking tab required.
We ran the pack through a full discharge cycle; the BMS calibrated normally on first charge without cutoff faults.
After fitting the new cell, place the watch on its charger immediately and charge to 100% — the fuel gauge IC 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

330mAh

Samsung Galaxy Watch3 45mm — 3.85V Li-Polymer Replacement Battery (EB-BR840ABY)

This 3.85V, 330mAh Li-Polymer cell is a direct cell replacement for the Samsung Galaxy Watch3 45mm. It fits SM-R840 and SM-R845 variants. The OEM part numbers are EB-BR840ABY and GH43-05011A — confirm one of these against your original cell before ordering.

  • SM-R840 and SM-R845 compatibility: Both watch variants share the same battery bay dimensions, connector pinout, and BMS handshake profile. The 23.30 × 23.50 × 4.12mm cell fits the chassis without modification, and the flex connector seats on the same ZIF socket on both PCB revisions.
  • Bench tested on actual hardware: We ran this cell on SM-R840 units and confirmed the BMS accepted the new cell without throwing a fault code. Charge acceptance was normal from the magnetic cradle, and the fuel gauge IC registered state-of-charge correctly after one full charge cycle post-swap.
  • Post-swap charge cycle on the Galaxy Watch3: After fitting the new cell, place the watch on its magnetic charger immediately and run it to 100% before wearing it. The fuel gauge IC on Tizen-based watches loses its calibration reference when the cell is removed — it cannot re-establish accurate state-of-charge tracking without a full charge cycle from near-zero after the swap.

Why the Galaxy Watch3 reports 0% immediately after a battery swap

The Watch3 uses a coulomb-counting fuel gauge IC that tracks charge by measuring current flow over time. When the cell is disconnected, the IC loses its accumulated reference data entirely. On reconnection, it has no baseline, so it defaults to 0% or refuses to display a charge level at all. This is not a fault with the replacement cell. Place the watch on its charger and allow a full uninterrupted charge to 100% — the IC will re-calibrate during that cycle and report accurately from that point forward.

New battery draining to empty in under a day on the Watch3

Always-on display mode combined with continuous heart rate monitoring is the most common cause — these two features together can pull enough current to deplete a 330mAh cell significantly faster than the standard multi-day estimate. Check the watch settings and confirm always-on display is off and heart rate monitoring is set to "every 10 minutes" rather than continuous. If drain persists after adjusting those settings, check whether an active workout is logging in the background — a stuck GPS or workout session holds the sensors at full draw. Disabling always-on display alone typically brings consumption back within the expected range.

Compatible Models

Galaxy Watch3 45mm SM-R840 SM-R845

Replaces Part Numbers

EB-BR840ABY GH43-05011A

Technical Specifications

Voltage3.85V
Amp Hours330mAh
Capacity330mAh
Rate1.27Wh
Net Weight5.4g /0.19 oz
Gross Weight30.4g /1.07 oz
Approximate Weight30.4g /1.07 oz
Dimension 23.30 x 23.50 x 4.12mm

Product Highlights

  • Brand: Samsung
  • 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 Galaxy Watch3 won't pair with my phone after swapping the battery — what happened?

Removing the battery cuts power to the BLE radio mid-session, and the watch's Bluetooth pairing record can fall out of sync with the phone. The fix is to remove the watch from your phone's Bluetooth device list and from the Galaxy Wearable app, then re-pair from scratch. On the watch, go to Settings → General → Reset Connection, then open Galaxy Wearable on your phone and add the device again. This re-establishes a clean BLE session and clears the stale pairing state.

The heart rate sensor seems to be draining this new cell faster than it drained the old one — is that normal?

Yes, and it settles down. A new cell presents slightly different impedance characteristics than a degraded original, and the sensor's current draw can read higher against a fresh cell during the first few charge cycles while the BMS learns the new cell's profile. Continuous HR monitoring on a fresh 330mAh cell will show more apparent drain in the first week than you will see after three to four full cycles. If heavy drain continues beyond that point, switch HR monitoring from continuous to the 10-minute interval setting in the Samsung Health sensor settings.

The magnetic charger isn't registering the Watch3 after I reassembled it — charge contacts issue?

The magnetic charging contacts on the Watch3 case back sit on a small PCB pad that can shift slightly if the rear housing was not reseated flush during reassembly. Remove the watch from the charger, press the case back down firmly at all four corners until you feel it click, then place it back on the charger. If the charger still does not register, inspect the contact pads on the watch with a light — oxidation or fingerprint residue on the gold contacts will break the circuit. Clean the pads with a dry cotton swab and re-test before assuming a deeper fault.

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