COMfortel M-520 Replacement Battery 3.7V 950mAh Li-ion

COMfortel M-520 / M-710 — 3.7V Li-ion Replacement Battery

This 3.7V, 950mAh Li-ion battery fits the COMfortel M-520 and M-710 cordless DECT handsets. It replaces the original cell when the handset no longer holds adequate charge between base visits. Dimensions are 52.95 × 35.10 × 4.50mm — confirm these against your existing cell before fitting.

• M-520 and M-710 compatibility: Both handsets share the same battery bay dimensions, connector pinout, and 3.7V Li-ion charging circuit in the base station, so one cell covers either model.
• Bench tested on actual hardware: We ran charge and discharge cycles through the M-520's base station circuit. The protection board handled overcharge cutoff cleanly at 4.2V and low-voltage cutoff triggered correctly before cell damage could occur.
• First charge after fitting: Place the handset in the base immediately after installing this battery and leave it for a full 16 hours before making calls. Li-ion cells shipped partially discharged — the base charging circuit needs an uninterrupted cycle to calibrate the charge state correctly.

Talk time shorter than expected after fitting a new Li-ion cell

A new Li-ion cell shipped from storage often arrives at 30–50% state of charge. If you make calls before completing a full charge cycle, the handset's fuel gauge starts from an inaccurate baseline. The base station then underestimates remaining capacity on subsequent charges. One full 16-hour charge from near-empty resets this and brings talk time up to the rated figure.

Base station charge light not activating with new battery installed

If the base shows no charge indicator after fitting, the battery voltage may be low enough that the base circuit treats it as an error state rather than a chargeable cell. Remove the handset, wait 10 seconds, and reseat it firmly — poor contact at the charging pins is a common cause. If the light still does not activate, check the battery voltage with a multimeter at the contacts; a reading below 3.0V means the cell discharged deeply in storage and needs a trickle charge before the base circuit will accept it.