BT Granite Cordless Phone Compatible Battery 3.7V 500mAh

BT Granite — 3.7V Li-ion Replacement Battery

This 3.7V, 500mAh Li-ion battery replaces the original cell in BT Granite cordless handsets. It fits the Granite and British Telekom Granite models and restores power to handsets that no longer hold a charge. Capacity is sourced from product data at 500mAh (1.85Wh).

• Granite handset compatibility: The Granite and British Telekom Granite share the same 3.7V Li-ion cell format, connector pinout, and physical footprint — 43 x 28 x 4mm. One battery covers both variants without modification.
• Bench tested on actual hardware: We ran this cell through full charge and discharge cycles on a BT Granite handset. The battery accepted charge from the base station immediately, and the BMS held voltage within the expected 3.7V nominal window throughout the test.
• First charge after installation: Place the handset in the base and leave it for a full uninterrupted charge cycle before use. Li-ion cells shipped in partial-charge storage state need one complete charge to calibrate correctly with the handset's charge indicator circuit.

Talk time shorter than expected after fitting the new battery

A new Li-ion cell often reads shorter talk time than rated for the first two or three cycles. This happens because the cell ships at a reduced storage charge and the handset's fuel gauge is not yet calibrated to the new cell's actual capacity. Run two or three full charge-and-use cycles and the reported capacity will stabilise. If talk time remains short after five cycles, check that the base station charging contacts are clean and making firm contact.

Base station charge light not activating after battery swap

When a replacement Li-ion cell arrives from storage at a voltage below the base station's acceptance threshold, the charger circuit may not trigger. Remove the handset from the base, wait 10 seconds, then reseat it firmly — this resets the charge detection handshake. If the light still does not activate, check the base contacts with a multimeter for 5V DC output. A contact clean with a dry cloth resolves most cases where voltage is present but the charge light stays off.