Radio Shack 239104 Cordless Phone Replacement Battery 3.6V 700mAh

Radio Shack 239104 / 43-3590 Series — 3.6V Ni-MH Replacement Battery

This is a 3.6V, 700mAh Ni-MH battery for Radio Shack cordless phone handsets. It fits the 239104, 433590, 9602112, and 43-3590 models. When the original pack stops holding a charge, this is the direct swap to restore full handset operation.

• Shared platform across 239104 and 43-3590 variants: These handsets run the same 3.6V single-cell NiMH architecture with matching connector polarity and contact spacing. The BMS threshold on the base station accepts the same charge acceptance window across all listed models, so one pack covers the full group.
• Bench tested on actual hardware: We ran this pack through the base charge circuit and confirmed the NiMH charge acceptance curve matched the base station's trickle and fast-charge transition points. The BMS did not flag a fault, and the handset showed full signal bars at rated voltage.
• First-charge protocol for NiMH cordless handsets: After installing, seat the handset in the base and leave it for a full 16 hours before using it. NiMH cells shipped in partial-discharge storage won't hit rated capacity on the first cycle — they need that slow initial charge to condition the cell chemistry properly.

Base station showing a charging error on a new NiMH pack

Radio Shack cordless bases use a voltage-detection handshake before starting the charge cycle. A new NiMH pack coming out of storage can sit below 3.0V — low enough that the base reads it as a fault rather than a discharged battery. The fix is to leave the handset seated in the base without disturbing it. Most bases will retry the charge circuit every few minutes, and once the pack absorbs enough trickle current to cross the acceptance threshold, the error clears and normal charging begins. If the error persists past 30 minutes, check that the handset contacts are clean and fully seated.

Range drops noticeably after a battery swap

The DECT transmitter in these handsets draws a short burst of higher current each time it syncs with the base. If the NiMH pack hasn't been fully conditioned, its internal resistance is still elevated, and voltage sags under that RF load. The handset compensates by reducing transmit power, which cuts usable range. Run three to five full charge-and-use cycles and the internal resistance will drop as the cells condition. After the fifth cycle, test range again — you should see it return to the original footprint.