Cobra AN-8521 Replacement Battery 3.6V 250mAh Ni-MH

Cobra AN-8521 / CP-479 Series — 3.6V Ni-MH Replacement Battery

This is a 3.6V 250mAh Ni-MH replacement battery for the Cobra AN-8521, CP-479, CP-479S, and CP-480 cordless phone handsets. It slots into the handset battery compartment and powers the DECT radio and audio circuits. Voltage and cell count match the original Cobra pack exactly.

• AN-8521 and CP-479 series compatibility: These handsets share the same 3.6V three-cell Ni-MH battery bay, connector orientation, and charge acceptance circuit. One pack covers the full model group without modification.
• Bench tested on actual hardware: We ran this pack through the Cobra charge circuit and confirmed the base station accepted the battery without throwing a charge error. The BMS handshake completed normally across multiple charge cycles.
• First-charge conditioning for Ni-MH handsets: After installing, seat the handset in the base and leave it for a full 16 hours before the first call. Ni-MH cells in cordless phones need a slow initial charge to reach rated capacity — skipping this shortens usable talk time from the first cycle.

Talk time shorter than rated after replacement

Ni-MH cells ship in a partial-discharge state. On the first few cycles, the cell chemistry hasn't fully activated, so measured capacity runs below the 250mAh rating. This is normal and not a fault with the pack. Capacity builds over three to five full charge-discharge cycles until the cells stabilise at rated output. If talk time is still short after five cycles, check that the handset is seated squarely in the base — a misaligned contact drops the charge current.

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

Cobra base stations check incoming battery voltage before starting the charge cycle. A Ni-MH pack that has self-discharged during storage can arrive below the acceptance threshold — typically under 3.0V — and the base reads this as a fault rather than a flat battery. Remove the handset, wait 30 seconds, and reseat it firmly. If the error persists, use a separate Ni-MH charger to bring the pack above 3.2V, then return it to the base for a normal charge cycle.