Apple Watch Series 1 MQL12LL/A Replacement Battery 3.82V 350mAh
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Apple Watch Series 1 MQL12LL/A Replacement Battery 3.82V 350mAh - is backordered and will ship as soon as it is back in stock.
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Battery Care Tips
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
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
⚠️ 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.
Apple Watch Series 1 MQL12LL/A Replacement Battery 3.82V 350mAh - is backordered and will ship as soon as it is back in stock.
Voltage
3.82V
Amp
350mAh
Apple Watch Series 1 — 3.82V Li-Polymer Replacement Battery (A1850)
This 3.82V, 350mAh lithium-polymer cell replaces the original A1850 battery in Apple Watch Series 1. It fits MQL12LL/A, MQL22LL/A, MQL42LL/A, MQL02LL/A, and 22 additional Series 1 variants. Swap it when the original cell no longer holds a charge or the watch shuts down under light load.
- Series 1 compatibility: All Series 1 models share the same 27.50 × 18.50 × 5.30mm cell footprint, the same flex connector tab, and the same BMS handshake parameters — so the A1850 part number covers the full Series 1 lineup regardless of case size or finish.
- Bench tested on actual hardware: We cycled this cell through charge and discharge on Series 1 hardware. The BMS accepted the new cell without error flags, and the fuel gauge re-registered correctly after a full charge cycle from near-zero.
- Fuel gauge reset after fitting: Place the watch on its magnetic charger immediately after seating the new cell and charge to 100% before first use. The fuel gauge IC on Series 1 loses its reference when the old cell is disconnected. Without a full charge from near-zero, it reports inaccurate state-of-charge from the first wake.
Why Series 1 shuts down at 20–30% after a cell swap
The Series 1 fuel gauge IC stores a charge table tied to the previous cell's impedance curve. When you fit a new cell, that table is stale. The IC reads voltage correctly but maps it to the wrong state-of-charge — so it triggers a low-battery shutdown while actual cell voltage is still above 3.5V. A full charge cycle from near-zero rewrites the table to match the new cell's curve and stops the early cutoff.
Magnetic charger not registering after reassembly
If the back cover shifts even slightly during reassembly, the charge contacts on the watch body no longer sit flush against the magnetic puck. The watch will not show the charging icon and the cell stays at whatever voltage it woke at. Press the back cover firmly until it clicks flat, then re-seat the charger. If the icon still does not appear, check that the flex connector tab is fully latched — a half-seated connector lets the watch power on but breaks the charge circuit.
Compatible Models
Replaces Part Numbers
Technical Specifications
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 1 shows 0% and won't turn on right after I put in the new battery — did I get a dead cell?
Almost certainly not. When you disconnect the old cell, the fuel gauge IC loses its charge reference entirely and wakes in an undefined state — it often reports 0% and refuses to boot until it has a fixed voltage anchor. Put the watch straight onto its magnetic charger and leave it until it reaches 100%. One full charge from near-zero gives the IC a new reference point, and the watch will power on normally from there.
The new battery is draining much faster than expected — the watch barely makes it through a day.
On a freshly fitted cell, always-on display combined with continuous heart rate monitoring creates a sustained current draw that can look like accelerated drain for the first few days. The fuel gauge IC is also still refining its capacity estimate across the first two or three full cycles. Turn off always-on display in Settings → Display & Brightness and disable continuous heart rate monitoring in Settings → Privacy → Health if you need to verify the cell is performing correctly — then re-enable them once the gauge has stabilised after three full charge-discharge cycles.
My Apple Watch won't pair with my iPhone after replacing the battery — Bluetooth keeps failing.
Removing the battery cuts power to the BLE stack mid-session, and the existing pairing session record on both devices can corrupt. Go to Settings → Bluetooth on your iPhone, tap the Watch entry, and select "Forget This Device." Then on the watch, go to Settings → General → Reset → Erase All Content and Settings, and re-pair from scratch in the Watch app. The pairing completes within a few minutes and restores all synced data from the paired iPhone backup.
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