COMfortel M-520 Compatible Battery 3.7V 830mAh Li-ion

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

This is a 3.7V 830mAh Li-ion battery for the COMfortel M-520 and M-710 cordless DECT handsets. It slots into the battery compartment on the rear of the handset and restores wireless operation when the original cell can no longer hold a charge. Capacity is 830mAh (3.07Wh) — matching the original specification.

• M-520 and M-710 compatibility: Both handsets share the same battery bay dimensions (52.95 × 35.10 × 4.50mm), the same 3.7V Li-ion chemistry, and the same charge circuit on the base station — so one cell fits both models without modification.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the base station cradle. The protection circuit responded correctly to charge cutoff at full voltage and tripped as expected on low-voltage discharge — no thermal events, no anomalous BMS behaviour.
• First-charge protocol for DECT Li-ion handsets: After installing, seat the handset in the base and leave it for a full uninterrupted charge cycle before first use. Li-ion cells shipped in storage-state need one complete charge to allow the BMS to calibrate its state-of-charge register accurately.

Talk time shorter than expected after fitting the new battery

A Li-ion cell arriving from storage often has a partial charge, and the BMS state-of-charge counter starts uncalibrated. The handset's fuel gauge reads inaccurately for the first cycle or two, which causes early low-battery warnings. Run two full charge-then-discharge cycles on the base, and the reported capacity will align with the actual 830mAh rating. If talk time is still noticeably short after three full cycles, check that the handset is fully seated — a loose contact causes trickle charging only.

Handset not re-pairing with the base after battery replacement

Removing the battery from a DECT handset cuts all power to the volatile memory holding the pairing data on some COMfortel models. When power is restored, the handset comes up with no registered base and shows an unregistered or searching indicator. Re-registration takes under two minutes — press and hold the registration button on the base unit until the LED flashes, then initiate pairing from the handset menu. Once confirmed, the handset stores the new pairing in non-volatile memory and retains it through future battery swaps.