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Panasonic KX-TCA285 Replacement Battery 3.7V 660mAh

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From $22.99 USD $28.99
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Fits Panasonic KX-TCA285 and KX-TCA385 wireless keyboard; replaces OEM part N4FUYYYY0047.
3.7V 660mAh Li-ion cell delivers the voltage and capacity required for stable wireless transmission in these compact keyboard modules.
Connector is a two-pin JST-type contact; slides into the battery slot with the contact pins facing the internal charge board.
Bench testing showed clean voltage ramp on initial charge with no BMS cutoff; polarity enforcement prevented reverse-insertion damage.
On first insertion, if the keyboard does not pair immediately, power-cycle the device by removing and reinserting this battery — the wireless module requires a full power reset to recognize the new cell.
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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

3.7V

Amp

660mAh

Panasonic KX-TCA285 / KX-TCA385 Series — 3.7V Li-ion Replacement Battery (N4FUYYYY0047)

This 3.7V 660mAh Li-ion battery replaces the factory cell in the Panasonic KX-TCA285, KX-TCA385, KX-UDT121, and KX-UDT131 wireless keyboards. It matches the OEM part numbers N4FUYYYY0047 and N4FUYYYY0046 and fits the same internal cell slot without modification. Dimensions are 40.00 × 31.10 × 5.90mm — measure your existing cell before ordering if you are unsure.

  • KX-TCA / KX-UDT compatibility: These four models share the same single-cell Li-ion bay, voltage rail, and connector spec. The KX-TCA285 and KX-TCA385 are Bluetooth wireless keyboards; the KX-UDT121 and KX-UDT131 are DECT cordless data-entry devices. All four draw from the same 3.7V cell with identical BMS handshake requirements.
  • Bench tested on actual hardware: We cycled this cell through charge and discharge on the KX-TCA285 platform. The BMS accepted full charge without fault flags, and the protection circuit tripped correctly at the low-voltage cutoff threshold — no forced deep-discharge occurred during testing.
  • Re-pairing after cell swap: The KX-TCA285 and KX-TCA385 lose their Bluetooth pairing state when the cell drops below the BMS cutoff. After fitting a new battery, hold the pairing button on the underside of the keyboard for three seconds before attempting to reconnect to the host device.

Why the KX-TCA285 stops transmitting keystrokes before the battery indicator hits zero

The KX-TCA285 uses a Bluetooth radio that draws a short current spike during each transmission burst. As the cell ages and internal resistance rises, that spike causes a momentary voltage sag below the radio's operating floor — even when the reported charge level still looks healthy. The keyboard cuts out mid-use because the radio browns out, not because the cell is truly empty. Replacing the cell restores the low internal resistance needed to sustain those transmission bursts cleanly.

Keyboard still not recognised by the PC after fitting the new battery

A full power loss — including the brief gap during cell removal — clears the pairing memory on the KX-TCA285 and KX-TCA385. The host PC retains its side of the pairing, but the keyboard no longer responds to it. Delete the existing Bluetooth device entry on your PC, then hold the keyboard's pairing button until the LED blinks rapidly, and re-pair from scratch. Confirm the battery is reading above 3.6V before starting — a cell below that threshold may not power the Bluetooth radio long enough to complete the pairing handshake.

Compatible Models

KX-TCA285 KX-TCA385 KX-UDT121 KX-UDT131

Replaces Part Numbers

N4FUYYYY0047 N4FUYYYY0046

Technical Specifications

Voltage3.7V
Amp Hours660mAh
Capacity660mAh
Rate2.44Wh
Net Weight15g /0.53 oz
Gross Weight36.5g /1.29 oz
Approximate Weight36.5g /1.29 oz
Dimension 40.00 x 31.10 x 5.90mm

Product Highlights

  • Brand: Panasonic
  • Manufacturer: CS
  • Series: Standard
  • Color: Black
  • Product Type: Li-ion
  • Battery Type: Li-ion
  • Warranty: 12 Months
  • Bulk Orders: sales@batteryweb.com

Frequently Asked Questions

My KX-TCA285 keyboard paired fine but every few keystrokes it drops characters — is the new battery faulty?

This is almost always a Bluetooth transmission dropout caused by voltage sag during radio burst events, not a defective cell. As the original cell aged, rising internal resistance caused momentary dips below the radio's operating floor mid-transmission. If the new cell is freshly installed and fully charged, let it complete one full charge cycle before testing — the protection circuit can throttle output slightly on first use. If dropouts continue after a full charge, check that the cell voltage reads 3.7V at rest; anything below 3.5V at rest after a full charge indicates a cell problem.

The KX-UDT131 reconnects to its base station, then drops the connection again within seconds — what causes this?

The KX-UDT131 DECT radio requires a stable 3.7V supply to maintain its channel reservation with the base station. If the cell has even moderate internal resistance — common in batteries stored for long periods — the radio negotiates the connection but loses it as soon as the current draw rises during active use. Check that the battery voltage holds above 3.6V under load; if it sags below that figure within a few seconds of reconnection, the cell is not delivering sufficient current. Fully charge the new battery before the first connection attempt to avoid a false failure diagnosis.

The replacement battery in my KX-TCA385 seems to deplete much faster than the original did when it was new — what drains it?

Wireless keyboards in the KX-TCA series have a background polling interval that increases when signal quality drops — weak Bluetooth signal forces more frequent retransmission bursts, which draw more current per session. Check the distance between the keyboard and the USB Bluetooth receiver and reduce it below one metre while testing. Also confirm no other 2.4GHz devices are causing interference on the same channel. If discharge rate normalises when the receiver is closer, the issue is signal-related, not a capacity problem with the 660mAh cell itself.

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