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FRITZ!Fon MT-F Cordless Phone Replacement Battery 312BAT006 3.7V

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New arrival
From $23.99 USD $29.99
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Fits FRITZ!Fon MT-F and AVM 2000 2446 handsets, replacing OEM part 312BAT006.
3.7V, 700mAh lithium-ion cell delivers adequate charge capacity for standard cordless phone operation.
Connector slides straight into handset battery slot with positive contact facing the spring terminal.
Bench testing showed clean BMS voltage ramp on first insertion with no base station rejection signals.
After install, seat the handset in base for a full 16-hour charge before regular use.
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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

700mAh

FRITZ!Fon MT-F Series — 3.7V Li-ion Replacement Battery (312BAT006)

This 3.7V, 700mAh Li-ion cell replaces part number 312BAT006 in the FRITZ!Fon MT-F, C4, and AVM 2000 2446 cordless DECT handsets. It fits the same footprint as the factory cell at 47.06 × 35.52 × 4.55mm. Install it when the original battery no longer holds a usable charge between base sessions.

  • MT-F and 2446 series fit: These handsets share the same battery bay dimensions, connector pinout, and 3.7V nominal charge rail — one cell covers the full listed model range without modification.
  • Bench tested on actual hardware: We cycled this cell through charge and discharge on the FRITZ!Fon platform. The BMS accepted full charge termination cleanly and held voltage within the handset's operating window across repeated sessions.
  • First-charge protocol for Li-ion in DECT handsets: Place the handset in the base immediately after fitting the new cell and leave it for a full uninterrupted charge before making any calls. FRITZ!Fon handsets top-balance the Li-ion cell through the base station's charge circuit — interrupting this first cycle can leave the reported charge level miscalibrated for several days.

Why the MT-F handset loses range after a battery swap

DECT transmit power draws short, sharp current spikes during RF bursts. A Li-ion cell that shipped with a partial state of charge can sag below the handset's transmit threshold under that load, causing the radio to step down power or drop sync with the base. This shows up as reduced range or choppy audio — not a pairing fault. A full charge cycle from the base station restores the cell to its working voltage and the range issue clears without any re-pairing.

Handset not pairing with base after battery replacement

Removing the battery cuts all power to the handset, which erases the active DECT pairing on some MT-F firmware versions. The base station retains its end of the registration, but the handset comes up blank. To fix this, press and hold the registration button on the base for at least three seconds, then navigate to the handset's menu and run a new DECT registration. The process takes under two minutes and restores the pairing without a full factory reset.

Compatible Models

MT-F 2000 2446 AVM 2000 2446 C4 M2 EM325 M325 EM25

Replaces Part Numbers

312BAT006

Technical Specifications

Voltage3.7V
Amp Hours700mAh
Capacity700mAh
Rate2.59Wh
Net Weight15g /0.53 oz
Gross Weight40g /1.41 oz
Approximate Weight40g /1.41 oz
Dimension 47.06 x 35.52 x 4.55mm

Product Highlights

  • Brand: FRITZ!Fon
  • 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 FRITZ!Fon MT-F talk time is much shorter than the original battery — is the new cell faulty?

Not likely. A Li-ion cell shipped from storage sits at a partial charge and the handset's fuel gauge needs at least two to three full charge-and-use cycles to recalibrate. Short talk time in the first few sessions is a calibration lag, not a cell fault. Run the handset down until the low-battery warning triggers, then charge uninterrupted in the base each time. By cycle three, reported and actual capacity align.

The base station charge light isn't coming on after I fitted the replacement battery — what's wrong?

A Li-ion cell at low storage voltage can fall outside the acceptance window the FRITZ!Fon base uses to confirm a valid pack is seated. Check the battery connector is fully clicked in — the MT-F connector can feel seated without making full contact. If the light still won't trigger, remove the battery, wait 10 seconds, and reseat it firmly. The base should detect the cell and begin charging within 30 seconds; if the charge indicator still doesn't appear, check that the base itself has mains power.

My FRITZ!Fon MT-F battery drains completely overnight even when the handset is in the base — why?

This points to the handset not making reliable contact with the base charging pins, not a cell fault. Standby draw on a DECT handset is low, but if the charge circuit isn't completing, the cell drains from standby alone by morning. Clean the charge contacts on both the handset and base with a dry cloth, then reseat the handset and confirm the charge indicator activates. If contact is good, verify the base has a stable mains connection — intermittent power to the base stops the charge cycle mid-session.

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