AT&T 401 Cordless Phone Replacement Battery 3.6V 700mAh

AT&T 401 / 4126 / 24032X — 3.6V Ni-MH Replacement Battery

This is a 3.6V, 700mAh Ni-MH battery pack for AT&T cordless phone handsets. It fits the 401, 4126, 24032X, and A36 series models. The pack slots into the handset battery compartment and connects to the existing charge contacts.

• 401 and 4126 series compatibility: These models share the same 3.6V single-cell NiMH format, the same footprint at 50.79 × 42.40 × 14.23mm, and the same two-contact charge interface — which is why one pack covers the full range without modification.
• Bench tested on actual hardware: We cycled this pack through the base station charge circuit on a 401 handset. The base accepted the NiMH voltage profile without a charge error, and the BMS held steady through full charge and idle draw.
• First charge on NiMH cordless packs: After installing, seat the handset in the base and leave it for a full 16 hours before first use. NiMH cells in cordless phones need that slow initial charge to condition the cells and reach rated capacity — a quick top-up will leave you with noticeably short talk time.

Talk time shorter than original battery after replacement

NiMH cells ship in a partially discharged state. The first three to five charge-and-use cycles are conditioning cycles — capacity builds each time. If talk time feels short after day one, that is expected behaviour, not a faulty pack. By cycle five, the battery should reach its rated 700mAh and hold it consistently.

Base station shows no charge or error light on new pack

NiMH packs that have sat in storage can drop below the voltage threshold the base station uses to detect a valid battery. The base interprets this as no pack present and will not start the charge cycle. Remove the handset, wait 10 seconds, and re-seat it firmly — this prompts the base to re-check voltage. If the error persists, the pack voltage has dropped too low; place a multimeter on the contacts and confirm you are reading at least 2.8V before re-seating.