Casio CP-1218 Cordless Phone Replacement Battery 3.6V 700mAh

Casio CP-1218 — 3.6V Ni-MH Replacement Battery

This is a 3.6V, 700mAh Ni-MH rechargeable battery for the Casio CP-1218 cordless handset. It slots directly into the handset battery compartment and restores power to the phone. No OEM part number exists for this cell, but it matches the voltage, capacity, and physical dimensions of the original pack.

• CP-1218 handset fit: The CP-1218 runs on a single-cell 3.6V Ni-MH pack at this exact footprint — 50.79 x 42.40 x 14.23mm. The base station's charging circuit is calibrated for Ni-MH chemistry at this voltage rail, so a Li-ion substitution would cause charging errors or overcharge damage.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on a Ni-MH-compatible test rig. The cell accepted a full charge without thermal event, and voltage held steady through multiple talk-load draw cycles before tapering at the expected low-voltage cutoff.
• First charge on a new Ni-MH cordless pack: After installing, seat the handset in the base and leave it there for a full 16 hours before first use. Ni-MH cells ship partially discharged and need a slow initial charge to reach rated capacity — skipping this step will make the first few cycles feel short.

Talk time shorter than the original battery after replacement

Ni-MH cells don't deliver full rated capacity on the first charge cycle — they need three to five full charge-discharge cycles to condition the cell chemistry. If talk time feels short straight out of the box, that's normal. Run the handset down until it signals low battery, then return it to the base for a full charge. Capacity builds with each cycle and typically stabilises by cycle four or five.

Base station shows no charge or error light after fitting new battery

Ni-MH packs can sit in storage for months and drop below the minimum voltage the base station's charge controller will accept — some Casio base units won't initiate a charge cycle if the incoming voltage reads too low. To recover, briefly connect a compatible external Ni-MH charger at the correct current rating to bring the cell above 3.0V. Once the resting voltage is back in range, return the handset to the base and the charge indicator should activate normally.