About this replacement
NEC MH240 — 3.7V Li-ion Replacement Battery (690021)
This 3.7V 1100mAh Li-ion battery replaces the original NEC part 690021 in the MH240 cordless handset. It slots into the battery compartment and connects to the same terminals as the factory pack. Voltage and cell dimensions match the MH240 exactly — 55.60 x 36.00 x 5.60mm.
- MH240 handset fit: The MH240 base station charges via contact pins on the handset cradle. This cell matches the voltage rail and physical footprint so the charging circuit sees the same load profile as the original pack.
- Bench tested on actual hardware: We cycled this battery on the MH240 handset and confirmed the BMS accepted charge from the base station without error codes. Voltage held steady through standby and active call draw.
- First-charge protocol for Li-ion cordless handsets: Place the MH240 in its base immediately after fitting this battery and leave it for a full uninterrupted charge before use. Li-ion cells shipped in storage state can read low voltage — the base station charger needs a complete cycle to calibrate the displayed charge indicator correctly.
Talk time shorter than expected after fitting the 690021 replacement
Li-ion cells arrive partially discharged from storage, typically around 3.0–3.2V. If you start using the handset before a full charge cycle completes, the usable capacity is lower than rated. The MH240 charge circuit also monitors voltage slope — an incomplete first charge means the base station may terminate charge early. Run two full charge-and-use cycles to let the pack reach its rated 1100mAh capacity.
MH240 handset not pairing with base after battery replacement
Removing the battery from a DECT handset clears volatile memory on some models, including stored pairing data. The MH240 may show an unregistered or searching status on the display after the swap. Re-register the handset using the base station registration button — hold it for three seconds until the base enters pairing mode, then follow the on-screen prompt on the handset. Once paired, the handset should connect within 30 seconds.