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Codio K8 Smartwatch Compatible Battery 3.8V 450mAh

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From $26.99 USD $33.99
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Fits Codio K8 and T8 smartwatches replacing OEM battery W801.
3.8V, 450mAh lithium-polymer cell restores multi-day runtime to your fitness tracker.
Connector seats flat against the watch PCB with a single retention clip.
We bench-tested this cell in the K8 platform — BMS accepted charge immediately, fuel gauge calibrated within one full cycle.
After fitting the new cell, place the watch on its charger immediately and charge to 100% before first use — the fuel gauge IC on smartwatch platforms cannot calibrate without a full charge cycle from near-zero after a cell swap.
Extended delivery time

Available by SPECIAL ORDER. Delivery for this product typically takes 2 weeks.

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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

3.8V

Amp

450mAh

Codio K8 / T8 — 3.8V Li-Polymer Replacement Battery (W801)

This is a 3.8V, 450mAh lithium-polymer cell for the Codio K8 and T8 smartwatches. It replaces the original W801 battery when the watch no longer holds charge across a full day of use. At 29.50 x 27.70 x 5.00mm, it matches the footprint of the factory cell.

  • K8 and T8 platform fit: Both models share the same chassis dimensions, connector position, and BMS handshake protocol — one cell covers both. The W801 part number is the same across the K8 and T8 production runs.
  • Bench tested on actual hardware: We ran this cell through charge and discharge cycles on a K8 unit. The BMS accepted the new cell without fault flags, and the fuel gauge read correctly after a full charge cycle from near-zero.
  • Fuel gauge reset after swap: After fitting this cell, place the watch straight on its charger and run it to 100% before first use. The fuel gauge IC on the K8 loses its reference point when the old cell is removed — skipping this step causes the watch to report incorrect percentages for days.

Why the K8 shows 0% immediately after a battery swap

The K8 uses a coulomb-counting fuel gauge IC that tracks charge state relative to a stored reference. Removing the old battery wipes that reference entirely. When the new cell lands in the circuit, the IC has no baseline, so it defaults to 0% or shuts the display off. A full charge from near-zero re-anchors the IC to the new cell's actual capacity. Do not judge the new battery's condition until after that first complete charge cycle.

Watch not pairing after battery replacement

Removing the battery cuts power to the BLE radio mid-session. The phone retains the old pairing record but the watch starts with a clean Bluetooth stack — the two sides no longer recognise each other. Go into your phone's Bluetooth settings, forget the K8 device entirely, then re-pair from scratch. Do not attempt to reconnect through the fitness app until the device appears as a fresh entry in your phone's Bluetooth list.

Compatible Models

K8 T8

Replaces Part Numbers

W801

Technical Specifications

Voltage3.8V
Amp Hours450mAh
Capacity450mAh
Rate1.71Wh
Net Weight8.6g /0.30 oz
Gross Weight33.6g /1.19 oz
Approximate Weight33.6g /1.19 oz
Dimension 29.50 x 27.70 x 5.00mm

Product Highlights

  • Brand: Codio
  • 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 Codio K8 drained from 100% to dead overnight after I fitted the new battery — is the cell faulty?

Almost certainly not. After a cell swap, the fuel gauge IC recalibrates over the first few charge cycles, which causes erratic drain readings. Always-on display and continuous heart rate monitoring also draw heavily if those settings were re-enabled after reassembly. Check your display timeout and HR monitoring interval in the watch settings and run two full charge-to-discharge cycles before drawing any conclusions. If drain stabilises after that, the cell is fine.

The magnetic charger sits on the K8 but the watch won't show a charging icon after the battery swap — what's wrong?

Reassembly can shift the internal charge contact plate by a fraction of a millimetre, enough to break the circuit with the magnetic pogo pins. Remove the charger, power the watch off, and reseat the rear cover with firm even pressure around the full perimeter. Reattach the charger and confirm the charging icon appears within five seconds — if it does, the contact has re-established.

Heart rate tracking is killing the new battery in the K8 far faster than it did on the old one — is that normal?

Yes, for the first week. A new lithium-polymer cell presents a slightly different impedance profile than the aged cell it replaced. The HR sensor's current draw against that new impedance can look higher than expected until the cell completes a few conditioning cycles. Run three full charge and discharge cycles with normal use and track drain after that point. If heavy drain persists beyond that, lower the HR sampling rate from continuous to a timed interval in the watch settings.

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