Extend-a-phone BT10 Replacement Battery 3.6V 600mAh Ni-MH

Extend-a-phone 52189A / 52298 Series — 3.6V Ni-MH Replacement Battery (BT10)

This is a 3.6V, 600mAh Ni-MH battery pack replacing part number BT10 in Extend-a-phone cordless handsets. It fits the 52189A, 52298D, 52298E, 52298F, and nine additional models in the same series. The pack slots into the handset battery compartment and restores wireless operation from the base station.

• 52189A and 52298 series compatibility: These models share the same 3.6V NiMH cell format, connector pinout, and charge-sense circuit. One BT10 pack covers all variants without modification.
• Bench tested on actual hardware: We cycled this pack through charge and discharge on a 52298-series handset. The BMS accepted charge from the base station cradle correctly, and the protection circuit tripped at the expected low-voltage cutoff without triggering a fault on the base.
• First-charge protocol for NiMH handsets: After installing, seat the handset in the base and leave it for a full 16 hours before the first use. NiMH cordless phone cells reach rated capacity only after a slow initial charge — skipping this step will leave the pack undercharged from day one.

Talk time shorter than the original battery after replacement

Fresh NiMH cells ship in a partially discharged state and need three to five full charge-discharge cycles before they hit rated capacity. On the first cycle, the pack may deliver noticeably less talk time than the original — that is normal cell behaviour, not a fault. Each subsequent cycle builds the electrochemical capacity closer to the rated 600mAh. Run the handset until the low-battery alert sounds, return it to the base for a full charge, and repeat for at least three cycles.

Base station charge light not activating after battery swap

NiMH packs that have sat in storage can drop below the voltage threshold the base charge circuit uses to confirm a valid battery is present. If the base shows no charge activity or an error light after fitting the new pack, remove the handset, wait ten seconds, and re-seat it firmly. If the base still does not respond, place the handset in the cradle for two hours — the trickle charge stage can recover a low-voltage pack enough to cross the acceptance threshold. Check for a solid or flashing charge indicator at the two-hour mark.