GP T306 Cordless Phone Replacement Battery 3.6V 400mAh

GP T306 — 3.6V Ni-MH Replacement Battery (T306)

This is a 3.6V, 400mAh Ni-MH replacement battery for cordless phone handsets using the T306 battery format. It replaces GP part numbers T306, 4M3EMJZ, and F6M3EMX. If your handset no longer holds a charge or drops out of range faster than it used to, this is the cell that brings it back.

• T306 format handsets: Cordless phones using this battery share the same 3.6V NiMH cell footprint, connector orientation, and voltage floor. The base station charger circuit expects this specific chemistry and voltage range — swapping in a lithium cell will not work and can damage the charging circuit.
• Bench tested on actual hardware: We ran this cell through a full charge-discharge cycle on a DECT handset base. The BMS accepted the cell without error, and charge current stepped down correctly at full capacity. Voltage held steady across multiple discharge cycles.
• First charge after installation: After installing, seat the handset in the base for a full 16-hour slow charge before first use. NiMH cells ship in a partially discharged state. Skipping this step leaves capacity on the table — the cell won't reach rated 400mAh until it completes a proper initial conditioning cycle.

Base station showing no charge or error light after battery swap

NiMH batteries lose voltage during storage. If the cell arrives below roughly 3.0V, some DECT base station charger circuits read it as a fault and refuse to begin charging. The base isn't broken — it's rejecting a cell that sits outside its acceptance window. Place the handset firmly in the base and leave it for up to 30 minutes; most chargers will attempt a trickle pre-charge to bring the voltage up before switching to full charge mode. If the error light clears within that window, the cycle has started normally.

Handset not re-pairing with base after battery replacement

Some DECT phones store pairing data in volatile memory that resets when power is fully removed — which is exactly what happens during a battery swap. The handset comes back up with no active link to the base. This is not a battery fault. Re-register the handset using your phone's pairing or registration procedure, typically held button on the base for 5–10 seconds, then confirm on the handset within 60 seconds.