T-Com Sinus 300 Cordless Phone Compatible Battery 3.6V 700mAh

T-Com Sinus 300 — 3.6V Ni-MH Replacement Battery

This is a 3.6V, 700mAh Ni-MH replacement battery for the T-Com Sinus 300 cordless DECT handset. It slots directly into the handset battery compartment and restores power to the handset for daily home or office use. No OEM part number exists for this cell, so match by model and voltage before ordering.

• Sinus 300 handset fit: The Sinus 300 runs a single 3.6V NiMH cell at 700mAh — the base station charges at a trickle rate tuned to that voltage window. A cell outside that voltage range will either trigger a charge error or sit uncharged in the cradle.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on a cordless phone test rig. The BMS on the base station accepted the cell from the first dock, and voltage held steady across the discharge curve without premature cutoff.
• First-charge protocol for NiMH cordless cells: After fitting this battery, seat the handset in the base and leave it for a full 16 hours before first use. NiMH cells shipped in partial charge states need that slow initial cycle to reach rated capacity — skipping it can permanently limit how much charge the cell accepts.

Talk time shorter than the original battery after replacement

NiMH cells leave storage with reduced capacity — this is normal chemistry, not a fault. The cell needs three to five full charge and discharge cycles before it reaches the 700mAh rated figure. Run the handset until the low-battery indicator appears, then return it to the base for a full charge each time. By cycle five, capacity should stabilise at or close to the rated level.

Base station showing no charge or an error light after fitting new cell

Cordless DECT bases check incoming voltage before committing to a charge cycle. A NiMH cell that has self-discharged in storage can drop below the base's acceptance threshold — typically around 3.0V — and the base reads it as a fault rather than a flat battery. Seat the handset firmly in the cradle for at least 30 minutes; most bases will begin a recovery trickle charge once the cell registers above that floor. If the error light clears within the hour, the cycle is working — leave the handset docked for the full 16 hours.