Casio 2500 Cordless Phone Replacement Battery 2.4V 750mAh

Casio 2500 / 2600 / T-2600 — 2.4V Ni-MH Replacement Battery

This is a 2.4V 750mAh Ni-MH rechargeable battery for the Casio 2500, 2600, and T-2600 cordless phone handsets. It slots into the handset battery compartment and restores the cordless operation lost when the original cell degrades. Voltage and cell format match the original pack exactly.

• 2500, 2600, and T-2600 compatibility: These three Casio cordless models share the same 2.4V dual-cell NiMH pack, handset connector orientation, and charge circuit timing. One battery fits all three because the base station charging circuit applies the same delta-V termination logic across the range.
• Bench tested on actual hardware: We cycled this pack through the Casio base station charge circuit and confirmed the BMS accepted charge without error, the voltage rose cleanly to termination, and the handset registered a full charge state.
• First-charge protocol for NiMH cordless handsets: After installing this battery, seat the handset in the base for a full 16-hour charge before first use. NiMH cells shipped in partial-discharge storage need a slow initial charge to reach rated capacity — cutting it short at 2–3 hours leaves cells below 750mAh on the first few cycles.

Range dropping mid-call after a new NiMH pack

DECT handsets regulate transmit power from the battery voltage rail. A new NiMH cell that hasn't completed its first full conditioning cycle has a lower usable voltage floor than a fully conditioned pack. Under RF transmit load, that voltage sags further — the handset pulls back transmit power to stay inside tolerance, and range shrinks. This is not a fault in the battery or the phone. Run three to five full charge-discharge cycles through normal use and the cell's internal resistance drops, voltage hold improves, and transmit range returns to normal.

Base station showing a charge error or refusing to charge after swap

Casio base stations use delta-V detection to confirm a NiMH pack is accepting charge — they look for a voltage rise from the resting level. A battery that sat in warehouse storage for months can drop below 2.0V per cell, which some base circuits read as a fault rather than a discharged pack. If the base shows an error light or won't initiate charging, remove the handset, wait 30 seconds, then reseat it firmly. If the error persists, trickle-charge the pack externally to 2.2V per cell before returning it to the base — this brings the voltage into the acceptance window the charge circuit expects.