Sony 5822 Cordless Phone Replacement Battery 3.6V 700mAh

Sony 5822 / 5823 / 5829 / 5845 Series — 3.6V Ni-MH Replacement Battery

This is a 3.6V, 700mAh Ni-MH rechargeable battery for Sony cordless phone handsets across the 5822, 5823, 5829, and 5845 series, plus over 43 additional compatible models. It replaces the original handset battery when the pack no longer holds a charge. The cell dimensions are 45.90 x 31.20 x 10.70mm — a direct physical match for the handset battery compartment.

• 5800-series handset compatibility: These Sony cordless models share a common 3.6V NiMH battery bay, identical connector orientation, and the same three-cell configuration across the platform. One battery SKU covers the full range without modification.
• Bench tested on actual hardware: We cycled this pack through charge and discharge on a 5822 handset base station. The BMS accepted charge immediately, the base charge indicator lit correctly, and the handset registered full signal within the first conditioning cycle.
• First-charge protocol for NiMH handsets: After installing the new pack, seat the handset in the base and leave it for a full 16 hours before first use. NiMH cells in cordless phones reach rated capacity only after a slow, uninterrupted initial charge — skipping this step leaves the pack permanently under-conditioned.

Base station showing no charge light after fitting a new NiMH pack

NiMH batteries sitting in storage can drop to voltages the base station's charge circuit won't initially recognise. The base expects a cell voltage above a minimum threshold before it begins the charge cycle. A pack below that threshold looks like an absent or faulty battery to the base. Place the handset in the base for 30 minutes — most Sony base stations will begin trickle-charging even a deeply discharged pack and the charge indicator will activate once the cell climbs above approximately 3.0V.

Talk time shorter than expected for the first few uses

NiMH cells require three to five full charge-discharge cycles before they reach rated capacity — this is normal cell chemistry, not a fault with the battery. During early cycles the electrodes have not yet fully activated, so usable capacity reads lower than the 700mAh spec. Run the handset until it prompts a low battery warning, return it to the base for a full charge, and repeat. By cycle five, talk time should stabilise at the rated level.