Sony BPT37 Cordless Phone Replacement Battery 3.6V 600mAh

Sony BPT37 / FF1185 Series — 3.6V Ni-MH Replacement Battery

This is a 3.6V 600mAh Ni-MH replacement battery for Sony cordless phones. It fits the BPT37, FF1185, FF1187, FF1188, and over 32 additional Sony handset models. The cell dimensions are 42.45 x 29.77 x 14.37mm — match these against your existing pack before ordering.

• FF1185 / BPT37 platform compatibility: These models share the same 3.6V single-cell NiMH rail, matching connector footprint, and base station charge contact layout. One replacement pack covers the full range without modification.
• Bench tested on actual hardware: We cycled this pack on a Sony cordless base and confirmed the charge circuit accepted the cell at the correct trickle rate. The NiMH chemistry topped out at the expected terminal voltage across three full charge cycles.
• First charge on a new NiMH pack: After installing, seat the handset in the base for a full 16-hour charge before use. NiMH cordless batteries ship with partial charge and won't reach rated capacity until the chemistry completes a slow, full first cycle.

Base station charge light not activating on a new NiMH pack

Sony cordless bases use a voltage-sense threshold to detect an inserted battery and start the charge cycle. A new NiMH pack can drop below that threshold after storage — the base reads no cell and the charge indicator stays off. Remove the handset, wait 10 seconds, and reseat it firmly so the charge contacts close cleanly. If the base still won't initiate, check the contact pins on the handset for oxidation and clean them with a dry cloth before reseating.

Range dropping when the NiMH pack is below half charge

DECT transmit power draws a short current spike when the handset locks onto the base frequency. An NiMH cell under RF load shows voltage sag — the lower the state of charge, the steeper the sag. When voltage dips below the handset's transmit floor, the RF output reduces and range falls noticeably. Keeping the handset in the base between calls avoids partial-discharge cycles and maintains the voltage headroom the transmit circuit needs.