Toshiba FD-9839 Cordless Phone Compatible Battery 2.4V 1200mAh

Toshiba FD-9839 / FD-9859 Series — 2.4V Ni-MH 1200mAh Replacement Battery

This is a 2.4V, 1200mAh Ni-MH replacement battery for Toshiba cordless phone handsets including the FD-9839, FD-9859, FD-9859BK, FT-8006A, and more than a dozen related models. It fits inside the handset and powers the DECT radio, speaker, and display. If your handset no longer holds a charge through a conversation, this is the cell that needs replacing.

• FD-9839 / FD-9859 handset family: These models share the same 2.4V two-cell Ni-MH pack format and handset connector. The base station's charging circuit is tuned to the Ni-MH charge curve, so the chemistry match matters — a Li-ion pack at this slot would confuse the trickle-charge termination logic.
• Bench tested on actual hardware: We cycled this pack through charge and discharge on a cordless phone test rig. The BMS accepted charge from a standard Toshiba base station without triggering an error state, and cell voltage held steady across the DECT transmit bursts we monitored.
• First charge after install: Place the handset in the base cradle for a full 16 hours before using it. Ni-MH cells ship partially discharged, and the slow overnight charge lets the chemistry reach rated capacity. Skipping this step is the most common reason a new battery underperforms from day one.

Base station showing a charging error after fitting a new Ni-MH pack

Ni-MH cells lose voltage during storage. If the resting voltage drops low enough, some Toshiba base stations flag an error rather than starting a charge cycle — the base interprets a very flat pack as a fault condition rather than a depleted battery. The fix is to briefly seat the handset, remove it for 30 seconds, then reseat it firmly. In most cases the base will then accept the pack and begin charging normally. If the error persists after two attempts, leave the handset seated for 10 minutes — some base stations will begin a recovery trickle charge once the pack voltage climbs above the acceptance threshold.

Handset loses pairing with the base after battery replacement

Removing a dead battery from a DECT handset cuts power completely, and several Toshiba models store pairing data in volatile memory — the link to the base is lost the moment power drops to zero. This is not a fault with the battery. Re-register the handset using the pairing button on the base station, typically held for three seconds until the base LED flashes. Check your handset manual for the exact key sequence, but on most FD-series units pressing and holding the FIND button on the base for five seconds starts the registration mode.