Sony FF2400 Cordless Phone Replacement Battery 3.6V 700mAh

Sony FF2400 / FF940 Series — 3.6V Ni-MH Replacement Battery

This is a 3.6V, 700mAh Ni-MH replacement battery for Sony cordless phone handsets including the FF2400, FF940, FF9915, and GH2400C, among others. It restores power to handsets where the original cell has degraded and can no longer hold a usable charge. Physical dimensions are 45.60 × 31.30 × 10.60mm — confirm these match your handset battery bay before ordering.

• FF2400 and FF940 series compatibility: These models share the same 3.6V single-cell NiMH format, connector orientation, and charging circuit expectations. One pack fits across all listed handsets because the base station charges at a fixed trickle rate matched to this cell chemistry and capacity.
• Bench tested on actual hardware: We ran this pack through charge acceptance and voltage recovery cycles on FF-series handsets. The cell accepted charge cleanly from a cold state and held above the 3.4V threshold the handset needs to maintain RF transmission.
• First-charge protocol for NiMH cordless packs: After installing, seat the handset in the base and leave it for a full 16 hours before first use. NiMH cells in cordless phones charge via slow trickle — a short first charge skips the conditioning needed to reach rated 700mAh capacity.

Range dropping after a battery swap in the FF2400

Cordless phone RF output is tied directly to supply voltage. When a NiMH pack hasn't been through conditioning cycles, its internal resistance is higher and voltage sags under the transmit load. The handset reads this sag as a low-battery state and reduces transmit power to compensate. Running three to five full charge-discharge cycles brings internal resistance down and stabilises the voltage rail under RF draw.

Base station shows no-charge or error light with a new NiMH pack

NiMH batteries sitting in storage self-discharge over time and can arrive below the voltage floor the base station checks before enabling its charging circuit. If the base shows no activity or an error light, the pack may be sitting below 3.0V. Remove the handset, wait 30 seconds, reseat it firmly, and confirm the charge contact pins on both the handset and base are clean and making solid contact. A pack at or above 3.0V should trigger the charging circuit within two minutes of seating.