T-Com Sinus A806 Compatible Battery 3.7V 1200mAh Li-ion

T-Com Sinus A806 — 3.7V Li-ion Replacement Battery

This is a 3.7V, 1200mAh Li-ion replacement battery for the T-Com Sinus A806 cordless DECT handset. It slots into the handset's battery compartment and restores wireless call capability when the original cell has degraded. Voltage and form factor match the stock battery at 53.00 x 34.00 x 5.70mm.

• Sinus A806 handset fit: The A806 uses a single-cell Li-ion pack at 3.7V nominal. The BMS in the handset monitors cell voltage directly — swap with a different voltage and the handset either refuses to power on or charges incorrectly. This cell matches that voltage rail exactly.
• Bench tested on actual hardware: We ran charge and discharge cycles through the Li-ion BMS and confirmed the protection circuit trips correctly at both high-voltage cutoff and low-voltage floor — no runaway charge, no hard shutdown during a normal call load.
• First charge after installation: Place the handset in the base cradle immediately after fitting this battery and leave it for a full uninterrupted charge cycle before using it. Li-ion cells shipped in storage state need one complete charge to initialise the onboard fuel gauge correctly.

Talk time shorter than the original battery after replacement

A new Li-ion cell arrives partially discharged from storage — typically between 40% and 60% state of charge. If you pull the handset off the base before the first full charge cycle completes, the fuel gauge reads from an uncalibrated baseline and cuts off early. Run one complete charge to 4.2V, then discharge through normal use, and repeat once more. After two full cycles the reported capacity aligns with the rated 1200mAh.

Handset loses DECT pairing after battery swap

Removing the battery on some DECT handsets wipes the pairing data stored in volatile memory — the Sinus A806 can exhibit this. The handset will show no base connection or display a registration error after power is restored. To fix it, re-register the handset from the base station menu: press the paging or register button on the base, then follow the handset's registration prompt. The process takes under two minutes and does not affect other registered handsets on the same base.