Southwestern Bell FF900 Cordless Phone Compatible Battery 3.6V 600mAh

Southwestern Bell FF900 / S60503 — 3.6V Ni-MH Replacement Battery

This is a 3.6V, 600mAh Ni-MH rechargeable battery for the Southwestern Bell FF900 and S60503 cordless phone handsets. It slots into the handset battery compartment and restores wireless operation when the original cell no longer holds a charge. Voltage and connector match the factory specification exactly.

• FF900 and S60503 compatibility: Both handsets run on the same 3.6V Ni-MH cell with identical connector orientation and physical footprint — 40 x 42 x 13.5mm. The base station charges through the same contact points regardless of which model you have.
• Bench tested on actual hardware: We cycled this pack through charge and discharge on a Ni-MH compatible bench tester. The cell accepted a full charge without voltage deviation and the base station registered a charging state on contact — no fault signal.
• First charge after installation: Seat the handset in the base immediately after installing this battery and leave it for a full 16 hours before use. Ni-MH cells ship in a partially discharged state — skipping this slow first charge will leave the pack short of its rated 600mAh capacity from day one.

Talk time shorter than expected after the first few uses

Ni-MH cells do not deliver full rated capacity in the first one to three cycles — this is normal electrochemistry, not a defect. The active material in each cell needs several full charge and discharge passes to reach stable capacity. On a fresh pack in the FF900, expect talk time to improve noticeably by cycle three or four. Run the handset until the low-battery alert sounds, then return it to the base for a full charge — repeat this three times before drawing conclusions about the battery's capacity.

Base station contact light not coming on after battery swap

A Ni-MH cell that has sat in storage for months can drop below the minimum voltage the base station needs to detect a valid battery — typically below 3.0V for a 3.6V three-cell pack. The base interprets this as an absent or faulty battery and shows no charge indicator. Remove the handset, wait 10 seconds, and reseat it firmly so both charge contacts are flush. If the light still does not appear, connect the base to mains power and leave the handset seated for 30 minutes — the trickle current will bring the cell voltage up to the acceptance threshold.