Mitel 5614 Cordless Phone Replacement Battery 3.7V 650mAh

Mitel 5614 / 5613 / 5603 / 5602 — 3.7V Li-ion Replacement Battery

This is a 3.7V 650mAh lithium-ion battery for the Mitel 5614, 5613, 5603, and 5602 cordless DECT handsets. It fits the internal battery bay on all four models and restores normal handset operation when the original cell has degraded. Capacity is 650mAh (2.41Wh), matching the factory specification.

• 5602 / 5603 / 5613 / 5614 shared platform: These four Mitel handsets share the same battery bay dimensions, connector pinout, and 3.7V supply rail. One cell services all four models without modification.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on a Mitel 5614 handset. The BMS accepted charge from the base station immediately, held the voltage rail stable under active DECT transmission, and tripped protection cleanly at low-cell threshold.
• First-charge protocol for Li-ion cordless handsets: Place the handset in the base station immediately after installing this battery. Allow an uninterrupted full charge before using the handset — the base charges at a low current rate that Li-ion cells need to complete their first cycle accurately.

Talk time shorter than original battery after replacement

A new Li-ion cell often shows reduced talk time for the first few cycles. The battery management system calibrates its state-of-charge tracking over several full charge and discharge cycles. Until that calibration settles, the handset may cut off earlier than expected. Run three to five full cycles — charge to completion in the base, then use until the handset signals low battery — and talk time will stabilise near rated capacity.

Base station not charging after battery swap

If the base station shows no charge indicator after fitting a new battery, the cell voltage from storage may be sitting below the base's acceptance threshold. Mitel base stations use a trickle pre-charge circuit to bring deeply discharged cells up before switching to the main charge current. Leave the handset seated in the base for at least two hours without removing it — the base needs uninterrupted contact to complete the pre-charge stage. If the charge indicator still does not appear after two hours, clean the handset charge contacts with a dry cloth and reseat it firmly.