Lucent Technologies E1937B Replacement Battery 3.6V 700mAh

Lucent Technologies E1937B / TL72108 Series — 3.6V Ni-MH Replacement Battery (27910)

This is a 3.6V, 700mAh Ni-MH battery for Lucent Technologies cordless DECT phone handsets. It fits the E1937B, E560-2, E560-5, E5912, and a wider range of TL-series handsets including the TL72108, TL72208, TL74108, TL74258, and TL74458. The OEM part numbers 27910, 5-2459, 5-2523, and B27910 all cross to this pack.

• TL and E-series handset compatibility: These Lucent handsets share a common 3.6V single-cell Ni-MH architecture, the same connector pinout, and matching physical dimensions of 46 × 31 × 10.50mm. Any handset in this family that accepted OEM part 27910 accepts this pack.
• Bench tested on actual hardware: We cycled this battery through charge and discharge on a TL-series handset base station. The NiMH chemistry accepted the trickle charge correctly, and the handset reported full charge status without error flags on the base unit.
• First-charge protocol for NiMH cordless handsets: After installing, seat the handset in the base for a continuous 16-hour charge before first use. NiMH cells in cordless phones need that slow initial charge to reach rated 700mAh capacity — cutting it short leaves the pack at 60–70% of what it should deliver.

Base station showing no charge or error light after fitting a new NiMH pack

A NiMH battery sitting in a warehouse loses voltage over time. If the resting voltage drops far enough, the base station's charge controller reads it as a fault rather than a depleted cell. Most Lucent bases use a delta-V detection circuit that expects the incoming pack to sit above roughly 3.0V before it begins the charge cycle. A pack at 2.6–2.8V from long storage can stall that handshake. Leave the handset seated for 30–60 minutes — many bases will begin a recovery trickle once the circuit sees the pack warming slightly. If the error persists past an hour, remove the battery, wait 10 seconds, and re-seat it to re-trigger the detection cycle.

Range dropping mid-call after replacing the battery

DECT transmit power draws a short burst of current each time the handset communicates with the base — more than the phone draws at idle. A NiMH pack in its first few cycles hasn't yet reached full electrochemical capacity, so voltage sags under that RF load. When voltage sags, transmit power drops, and range shrinks. This corrects itself across cycles three to five as the cells condition. Run three full charge-and-use cycles without interrupting the charge, and range returns to the level the handset was built for.