Telekom Speedphone 700 Replacement Battery 3.7V 1200mAh

Telekom Speedphone 700 — 3.7V Li-ion Replacement Battery

This is a 3.7V 1200mAh Li-ion battery for the Telekom Speedphone 700 cordless DECT handset. It slots into the handset's battery bay and restores power to a unit that no longer holds a charge. Capacity is 4.44Wh, matching the original cell specification.

• Speedphone 700 fit: The Speedphone 700 uses a slim single-cell Li-ion pack at 3.7V nominal — the same voltage rail the handset's charge management IC expects. The cell dimensions are 62.18 × 38.14 × 4.50mm. Any deviation in thickness will prevent the back cover from seating correctly.
• Bench tested on actual hardware: We cycled this cell through a full discharge and charge sequence on the Speedphone 700 platform. The charge IC accepted the cell without error, and the handset returned to normal standby behaviour within one complete cycle.
• Fuel gauge recalibration after install: After fitting this cell, run one full discharge from 100% down to automatic shutdown, then charge uninterrupted to 100% before normal use. The Speedphone 700's fuel gauge IC is calibrated to the old cell's discharge curve — this single cycle resets it against the new cell and stops erratic percentage readings.

Why the Speedphone 700 reports wrong battery percentage after a cell swap

The handset uses a fuel gauge IC that tracks charge state by comparing current draw against a stored discharge curve from the original cell. A new cell has a different internal resistance and a slightly different voltage-to-capacity slope. Until the IC learns the new curve, the percentage display drifts — often reading 40% remaining when the cell is nearly empty. One complete uninterrupted discharge-charge cycle lets the IC map the new cell and recalibrate its coulomb counter. After that cycle, the percentage display stabilises.

Speedphone 700 shuts off suddenly at 20–30% charge remaining

This is a voltage cliff issue, not a capacity problem. When the cell voltage drops below roughly 3.4V under the load of an active DECT transmission, the handset's protection circuit cuts power before the display reaches 0%. A worn original cell hits this cliff early because its internal resistance is high — it loses voltage fast under load even when the resting voltage looks acceptable. Fit the replacement, run one full recalibration cycle, and confirm the handset no longer drops out during calls. If shutdown still occurs early, check that the battery contacts in the bay are clean and making full contact — measure resting voltage at the terminals, which should sit above 3.6V when charged.