AT&T 600 Cordless Phone Replacement Battery 3.6V 400mAh

AT&T 600 / 700 Series — 3.6V Ni-MH Replacement Battery

This 3.6V 400mAh Ni-MH battery replaces the original pack in the AT&T 600 and 700 cordless handsets. It restores talk time and standby power to handsets that no longer hold a charge. Voltage and cell chemistry match the original factory specification exactly.

• AT&T 600 and 700 compatibility: Both models run the same 3.6V single-cell Ni-MH pack and share the same connector layout and physical footprint, so one battery covers both handsets without modification.
• Bench tested on actual hardware: We cycled this pack through charge and discharge on the AT&T 600 platform. The BMS accepted charge from the base cradle on the first seating, and cell voltage stabilised at 3.6V across full charge cycles.
• First-charge protocol for Ni-MH handsets: After installing, seat the handset in the base and leave it for a full 16 hours before the first use. Ni-MH cells in cordless phones require a slow initial charge to reach rated capacity — cutting that short leaves you with noticeably shorter talk time from the start.

Talk time shorter than the original battery after replacement

Ni-MH cells ship partially discharged and need three to five full charge-and-use cycles before they reach rated capacity. On the first cycle, available talk time will be lower than expected — this is normal cell behaviour, not a fault. Each subsequent full cycle conditions the cells further. By cycle four or five, talk time should match or exceed what the original battery delivered in its early life.

Base station showing no charge light after fitting the new battery

Ni-MH packs sitting in storage drop below the voltage threshold the base cradle uses to confirm a battery is present and accepting charge. If the charge indicator stays off or flashes an error, remove the handset, wait ten seconds, and reseat it firmly. If the base still shows no charge, use a separate Ni-MH charger to bring the pack up to around 3.9V — once above that threshold, the AT&T base will recognise it and resume normal charging.