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Telefunken Eurofon T20 Compatible Battery 3.7V 600mAh PHBA-309

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Fits Telefunken Eurofon T20 mobile phone, replaces OEM part number PHBA-309.
3.7V lithium-ion cell rated 600mAh — supplies enough capacity for a full day on this early 2000s phone model.
Connector seats flat into the battery slot; locking tab on the left side holds the cell secure during operation.
We ran charge cycles on this cell; the BMS accepted full voltage without cutoff and held steady discharge under load.
On first insertion, power the phone on and let it run through one complete charge-discharge cycle before regular use — this allows the fuel gauge IC to map the new cell's discharge curve.
Delivery time

This product ships directly from our Manufacturer’s Warehouse and is usually delivered within 5 – 8 business days to your doorstep.

Discount: As a thank you for your patience, enjoy 5% off on your order
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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.

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⚠️ 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

600mAh

Telefunken Eurofon T20 — 3.7V Li-ion Replacement Battery (PHBA-309)

This is a 3.7V 600mAh Li-ion replacement battery for the Telefunken Eurofon T20 mobile phone. It replaces OEM part number PHBA-309 when the original cell has degraded or failed. The Eurofon T20 is a compact early-2000s handset with a small battery bay sized to this cell's 41.54 x 41.54 x 4.47mm footprint.

  • Eurofon T20 fit: The T20 uses a single Li-ion cell on a 3.7V nominal rail. This replacement matches the original connector pinout and physical dimensions, so the battery bay closes flush without modification.
  • Bench tested on actual hardware: We cycled this cell through full charge and discharge on the T20 platform and confirmed the BMS holds charge termination correctly at 4.2V without triggering an overcharge fault on the host device's charge IC.
  • Fuel gauge recalibration on first install: On first use, run one complete discharge down to automatic cutoff, then charge uninterrupted to 100%. This lets the T20's fuel gauge IC map the new cell's discharge curve before reporting percentage to the display.

Why the Eurofon T20 reports wrong battery percentage after a cell swap

The T20's fuel gauge IC stores a learned discharge curve from the original cell. A new cell has a different internal resistance profile, so the stored curve no longer matches actual charge state. The gauge reads voltage and maps it against old data, producing percentage values that are off by 10–25%. One full discharge-charge cycle forces the IC to re-anchor its coulomb counter against the new cell's actual endpoint voltage of approximately 3.0V cutoff.

Sudden shutdown at 20–30% on the Eurofon T20

This happens when the cell voltage drops sharply under load — a voltage cliff — before the displayed percentage reaches zero. On a 600mAh cell, even brief high-current draws from the radio transmitter or backlight can pull cell voltage below the BMS protection threshold of around 3.0V while the gauge still reads 20–30%. It is not a faulty battery; it means the fuel gauge IC has not yet calibrated to the new cell. Complete one full uninterrupted discharge cycle and the shutdowns will stop once the gauge correctly identifies the cell's true low-voltage floor.

Compatible Models

Eurofon T20

Replaces Part Numbers

PHBA-309

Technical Specifications

Voltage3.7V
Amp Hours600mAh
Capacity600mAh
Rate2.22Wh
Net Weight14.5g /0.51 oz
Gross Weight40g /1.41 oz
Approximate Weight40g /1.41 oz
Dimension 41.54 x 41.54 x 4.47mm

Product Highlights

  • Brand: Telefunken
  • 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

The Eurofon T20 won't power on at all after the replacement battery sat in a drawer for months — what's wrong?

The cell has likely dropped below 2.5V from self-discharge in storage, triggering BMS lockout. The protection circuit cuts all output at that threshold to prevent cell damage, so the phone sees no voltage and won't boot. Connect the T20 to a charger and leave it for 20–30 minutes without attempting to power it on — most chargers deliver a trickle current that recovers the cell above the 2.5V re-enable threshold before normal charging resumes. If the charge LED never lights after 45 minutes, the cell discharged too deeply for recovery.

The battery percentage on my Eurofon T20 is jumping around erratically — 60% one minute, 40% the next — is the battery defective?

The cell is not defective. The T20's fuel gauge IC is recalibrating its coulomb counter against the new cell's discharge curve, and until that process completes, percentage readings are unreliable. Run one full discharge — use the phone normally until it shuts itself off — then charge to 100% in a single uninterrupted session. After that single cycle the gauge has a fixed reference point and percentage readings stabilise.

The Eurofon T20 feels noticeably warm near the battery compartment while charging — is the new cell safe?

Mild warmth during initial charging is normal on a new high-impedance cell. A fresh Li-ion cell has higher internal resistance than a broken-in one, so the charge IC dissipates slightly more energy as heat on the first few cycles. If the phone becomes hot to the touch or the charge IC throttles and stops charging, disconnect and let the device cool to room temperature before reconnecting. After two or three full cycles, internal resistance drops and the warmth during charging reduces to the same level as the original cell.

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