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Apple Watch Series 5 44mm A2181 Replacement Battery 3.82V

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From $26.99 USD $33.99
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Fits Apple Watch Series 5 44mm and Watch SE2 44mm, replaces OEM part A2181.
Voltage is 3.82V at 290mAh capacity, delivering full-day runtime on the Watch Series 5 platform.
Connector is the proprietary magnetic pogo pad; orientation locks to the watch body's charge contact alignment.
We bench-tested this cell on Series 5 hardware; BMS accepted charge curve at 0.5C with no early cutoff.
After fitting the new cell, place the watch on its charger immediately and charge to 100% before first use — the fuel gauge IC cannot calibrate without a full charge cycle from near-zero after a cell 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

3.82V

Amp

290mAh

Apple Watch Series 5 44mm — 3.82V Li-Polymer Replacement Battery (A2181)

This is a 3.82V, 290mAh Li-Polymer cell built to the A2181 specification. It fits the Apple Watch Series 5 44mm and Watch SE2 44mm, including MWVF2LL/A and MWW12LLA variants. Swapping this cell restores charge capacity lost to cycle degradation in the original battery.

  • Series 5 and SE2 44mm compatibility: Both models share the same 27.10 x 20.50 x 4.60mm cell footprint, flex connector pinout, and BMS handshake protocol — which is why a single A2181 cell covers both platforms.
  • Bench tested on actual hardware: We cycled this cell through the S5 PMIC on the bench. The BMS initialised correctly, charge current stepped down as expected at the CV phase, and no over-voltage events were logged.
  • Post-swap charging requirement: After fitting this cell, place the watch on its magnetic charger immediately and charge to 100% before first use. The fuel gauge IC loses its reference point during a cell swap and cannot recalibrate until it completes a full charge cycle from near-zero.

Why the Series 5 fuel gauge reads incorrectly after a cell swap

The Series 5 uses a coulomb-counting fuel gauge IC that tracks charge state relative to a stored battery profile. When the cell is removed, that reference is lost. The IC then estimates state-of-charge from open-circuit voltage alone, which produces inaccurate readings — often 0% or a sudden drop mid-day. A full charge cycle from near-zero lets the IC re-anchor its count to known endpoints and restore accurate percentage reporting.

Watch not pairing with iPhone after battery replacement

Removing the battery clears the active BLE session between the watch and iPhone. The watch reboots without a live pairing context, so the iPhone treats it as an unknown device. This is not a fault with the new cell. Open the Watch app on the iPhone, tap your watch, select "Unpair Apple Watch," then re-pair from scratch — the process takes under five minutes and restores full connectivity.

Compatible Models

Watch Series 5 44mm MWVF2LL/A MWW12LLA Watch SE2 44mm

Replaces Part Numbers

A2181

Technical Specifications

Voltage3.82V
Amp Hours290mAh
Capacity290mAh
Rate1.11Wh
Net Weight5g /0.18 oz
Gross Weight30g /1.06 oz
Approximate Weight30g /1.06 oz
Dimension 27.10 x 20.50 x 4.60mm

Product Highlights

  • Brand: Apple
  • 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 Apple Watch Series 5 shows 0% and won't turn on right after I put the new battery in — did I get a dead cell?

Almost certainly not. The fuel gauge IC loses its charge reference when the original cell is removed, so it reads 0% from open-circuit voltage alone. Place the watch flat on its magnetic charger and leave it until the display shows 100%. After that first full cycle, the gauge recalibrates and percentage readings stabilise.

The new battery is draining completely by mid-afternoon — the old one lasted all day even when it was worn out. What's wrong?

Always-on display combined with continuous heart rate monitoring pulls significantly more current than the watch draws in standby. If you upgraded to watchOS features that enable those sensors permanently, the draw profile changed — not the cell. Turn off always-on display in Settings → Display & Brightness and set heart rate monitoring to automatic rather than continuous. Check battery usage in the Watch app to confirm which app or sensor is leading the drain.

The magnetic charger doesn't seem to be making contact since I reassembled the watch — the charging animation never appears. What should I check first?

The most common cause is the rear cover shifting slightly during reassembly, misaligning the charge contacts by a fraction of a millimetre. Remove the watch from the charger, press the rear cover firmly and evenly until it seats flush, then re-place it on the charger. If the animation still does not appear, clean both the charger puck and the watch contact ring with a dry cloth — oxidation or adhesive residue on either surface breaks the inductive coupling.

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Apple Watch Series 5 44mm Replacement Battery, 3.82V, 290mAh, Li-Polymer 1

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