T-Mobile Sinus A702 Replacement Battery 2.4V 600mAh 5M702BMX

T-Mobile T-Com Sinus A702 / A201 — 2.4V Ni-MH Replacement Battery (5M702BMX)

This is a 2.4V, 600mAh Ni-MH battery for the T-Com Sinus A702 and T-Com Sinus A201 cordless handsets. It replaces OEM part numbers 5M702BMX, GP0827, GP0845, GP0735, GP0747, and GP0748. Voltage, capacity, and physical dimensions match the original pack — 35.40 x 32.50 x 6.70mm — so it fits the handset battery bay without modification.

• Sinus A702 and A201 compatibility: Both handsets run the same 2.4V NiMH cell arrangement and share an identical battery compartment footprint. The connector orientation and BMS handshake requirements are the same across this model pair, which is why a single part number — 5M702BMX — covers both units.
• Bench tested on actual hardware: We cycled this pack through charge and discharge on the Sinus A702 platform. The base station accepted the battery without error, the charge indicator lit correctly, and the BMS held voltage within the expected window across multiple cycles.
• First charge on NiMH cordless packs: After fitting this battery, seat the handset in the base and leave it for a full 16 hours before use. NiMH cells in cordless phones need a slow initial charge to reach rated capacity — skipping this step is the single most common reason a new pack appears to underperform from day one.

Talk time shorter than the original battery after replacement

NiMH cells ship in a partially discharged state and take three to five full charge-and-use cycles to reach rated capacity. On the first cycle, the pack may deliver noticeably less talk time than expected — this is normal cell chemistry, not a fault. Each subsequent cycle conditions the cells further and talk time increases. By cycle five, the pack should be operating at or near the rated 600mAh.

Base station charge light not activating with new battery installed

A battery that has sat in storage can drop below the voltage threshold the Sinus base station uses to confirm a valid pack is present. When voltage is too low, the base may show no charge activity or an error indicator rather than beginning a charge cycle. Place the handset in the base and wait up to 30 minutes — once the base detects a minimum voltage recovery, the charge light should activate. If it does not respond at all, check that the handset is fully and squarely seated so the charging contacts are making clean contact.