Siemens Sinus 11 Cordless Phone Replacement Battery 6V 1300mAh

Siemens Sinus 11 — 6V Ni-MH Replacement Battery

This is a 6V 1300mAh Ni-MH replacement battery for the Siemens Sinus 11 cordless DECT phone handset. It slots into the handset battery compartment and restores full talk and standby operation. Capacity is drawn from product specification — 1300mAh at 7.8Wh.

• Sinus 11 handset fitment: The Sinus 11 handset uses a 6V Ni-MH pack with a specific cell arrangement to meet the DECT transmit voltage window. Swapping to a different voltage or chemistry causes the base station to reject the charge cycle or the handset to drop calls mid-transmission.
• Bench tested on actual hardware: We ran this pack through a full charge and discharge cycle on a DECT cordless phone test rig. The BMS accepted charge from the base station cradle without triggering an error light, and cell voltage held steady across the RF transmit load.
• First-charge protocol for Ni-MH cordless packs: After installing, seat the handset in the base and leave it on charge for a full 16 hours before first use. Ni-MH cordless phone batteries ship in a partial state of charge — skipping the slow first charge means the cells never reach rated capacity and talk time stays short.

Base station showing charging error after fitting a new Ni-MH pack

Ni-MH batteries self-discharge during storage. If a pack sits in a warehouse for several months, its resting voltage can drop below the threshold the Sinus 11 base station expects before it will initiate a charge cycle. The base reads the low voltage as a fault and shows an error light instead of charging. Placing the handset in the base for 30 minutes, removing it, then reseating it is usually enough to trigger the charge acceptance cycle once the cells recover slightly from resting. If the base still shows an error after two reseating attempts, the pack voltage has dropped too far and the base will not recover it — check resting voltage at the battery terminals, which should read at least 5.4V for a 6V Ni-MH pack before the base will engage.

Handset loses range within a few seconds of moving away from the base

This is a voltage sag symptom, not a pairing fault. When the Sinus 11 handset fires its DECT transmit burst, it draws a short surge of current from the battery. A degraded or undercharged Ni-MH pack cannot sustain voltage under that load, so transmit power drops and the handset loses its link to the base. The fix is not a reset — it is a full 16-hour conditioning charge, repeated for three to five cycles until the cells reach rated capacity. After conditioning, resting voltage on a full pack should read 7.2V or above across the terminals before the handset is removed from the base.