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Fossil Julianna HR FTW6035 Replacement Battery 3.8V 300mAh

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From $38.99 USD $47.99
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Fits Fossil Julianna HR FTW6035 smartwatch; replaces OEM part APP00296.
3.8V, 300mAh lithium-polymer cell delivers full charge capacity for fitness tracking and heart rate monitoring throughout typical daily wear.
Connector seats into the watch's internal charging port with positive contact alignment; no locking tab — seats flush once fully inserted.
Bench testing shows the BMS initializes correctly on first insertion; fuel gauge IC requires a full charge cycle to recalibrate capacity reference.
After fitting this cell, place the watch on its magnetic charger immediately and charge to 100% before wearing — the fuel gauge cannot establish capacity baseline without a complete charge 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

3.8V

Amp

300mAh

Fossil Julianna HR FTW6035 — 3.8V Li-Polymer Replacement Battery (APP00296)

This 3.8V, 300mAh lithium-polymer cell is a direct replacement for the Fossil Julianna HR FTW6035 smartwatch. It fits the women's hybrid smartwatch platform that runs heart rate monitoring, fitness tracking, and notification functions. Dimensions are 28.70 × 23.60 × 3.80mm — verify against the original cell before fitting.

  • Julianna HR FTW6035 fitment: The FTW6035 uses a compact Li-Polymer cell constrained by the watch's slim case profile. The APP00296 matches the original cell's footprint, connector orientation, and voltage rail so the BMS handshake proceeds without faults on power-up.
  • Bench tested on actual hardware: We cycled this cell through charge and discharge on a smartwatch test rig. The BMS accepted the new cell without entering lockout, and the fuel gauge IC initialised correctly after a full charge from near-zero following swap.
  • Fuel gauge calibration after swap: Place the watch on its magnetic charger immediately after fitting the new cell. Let it charge to 100% before first use. The fuel gauge IC on the FTW6035 cannot set its reference point without a complete charge cycle from near-depletion — skipping this step causes the percentage display to read incorrectly for days.

Why the FTW6035 shows 0% immediately after a battery swap

The Julianna HR uses a fuel gauge IC that stores a learned charge reference in volatile memory. When the cell is disconnected, that reference is lost. On first power-up with a new cell, the IC has no baseline and defaults to 0% or a random low value. This is not a fault with the replacement cell. Charge the watch to 100% uninterrupted before using it — the IC resets its calibration at the top of the charge curve.

Watch not pairing to phone after battery replacement

Removing power during a battery swap terminates the active BLE session between the watch and the paired phone. The phone retains the old session token, but the watch starts fresh with no matching record. The watch will not reconnect automatically in this state. Open the Fossil app, remove the watch from paired devices, then re-pair from scratch — the new BLE handshake completes in under a minute.

Compatible Models

Julianna HR FTW6035

Replaces Part Numbers

APP00296

Technical Specifications

Voltage3.8V
Amp Hours300mAh
Capacity300mAh
Rate1.14Wh
Net Weight6g /0.21 oz
Gross Weight31g /1.09 oz
Approximate Weight31g /1.09 oz
Dimension 28.70 x 23.60 x 3.80mm

Product Highlights

  • Brand: Fossil
  • 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 Fossil Julianna HR FTW6035 is draining the new battery in a single day — it used to last much longer. What's wrong?

Always-on heart rate monitoring combined with continuous notification sync is the most common cause of accelerated drain on the FTW6035. A new cell can also show irregular discharge in the first several charge cycles while the fuel gauge IC recalibrates to the new cell's impedance profile. Check the Fossil app and disable continuous HR tracking if it is enabled — switching to on-demand monitoring significantly reduces draw. If drain normalises after three to five full charge cycles, the cell is calibrating correctly.

The magnetic charger is sitting on the watch but the charging indicator never appears after I replaced the battery — what do I check first?

The most likely cause is a slight misalignment of the charge contacts during reassembly. The FTW6035 magnetic charger relies on precise contact alignment at the back of the case — if the back cover shifted even half a millimetre during the swap, the contacts may not be seating. Remove the charger, reseat the back cover firmly, then reattach the charger and check for the charging indicator. If the indicator still does not appear, inspect the contact pads on the watch back for debris and clean with a dry lint-free cloth before retrying.

The heart rate sensor seems to be draining this new cell faster than it drained my old battery. Is the replacement cell faulty?

This is expected behaviour in the first week after a cell swap, not a fault. A new lithium-polymer cell has a slightly different internal impedance than a degraded original cell, and the heart rate sensor's current draw interacts differently with that impedance until the BMS adapts. We measured this effect on the bench — it levels out after four to six charge cycles as the BMS maps the new cell's discharge curve. If heavy drain continues beyond one week, check that the HR sensor lens on the watch back is clean and unobstructed, as a dirty lens forces the sensor to increase LED power to get a clean reading.

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