Sony BP-T26 Cordless Phone Replacement Battery 3.6V 600mAh

Sony BP-T26 — 3.6V Ni-MH Replacement Battery (BP-T26)

This is a 3.6V, 600mAh Ni-MH battery built to replace the original BP-T26 pack in Sony cordless phone handsets. It fits the SPP-22H, SPP-55H, S60503, and related models in that handset family. Swap it in when the original pack no longer holds a useful charge between calls.

• SPP-22H, SPP-55H, and S60503 series: These handsets share the same 3.6V single-cell NiMH bay and connector pinout, which is why one battery pack covers the range. The base station charger circuit is calibrated for this voltage and cell chemistry — swapping to a different chemistry will throw a charge error.
• Bench tested on actual hardware: We cycled this pack through charge and discharge on a cordless phone platform. The BMS accepted the NiMH charge profile without error on the base station, and voltage held steady through the full discharge curve under typical handset standby and talk loads.
• First charge on NiMH cordless packs: After installing, seat the handset in the base and leave it for a full 16 hours before first use. NiMH cells in storage lose charge unevenly across the cell group — a slow first charge brings all cells to the same state and lets the pack reach its rated 600mAh capacity.

Base station charge error on a freshly installed NiMH pack

Sony base stations use a delta-V detection circuit to confirm a NiMH pack is accepting charge. If the pack voltage is too low from storage, the charger may not register a valid battery and will flash an error instead of charging. This is not a fault with the base or the battery — it is the circuit rejecting a pack it cannot read correctly. Place the handset firmly in the base and leave it undisturbed for several hours; as the pack warms slightly, the charger circuit will often detect the rising voltage and begin the full charge cycle. If it does not, remove the handset, wait 10 minutes, and reseat it.

Talk time shorter than expected for the first several uses

NiMH cells arrive from storage partially discharged and unevenly matched across the cell group. The pack will not deliver its full 600mAh on the first or second cycle — this is normal chemistry, not a defective battery. Each full charge and discharge cycle conditions the cells and brings capacity closer to rated spec. Allow three to five full charge and discharge cycles before comparing talk time to the original battery.