Phone Mate SL4 Ni-MH Cordless Phone Replacement Battery 3.6V 600mAh

Phone Mate SL4 / SL5 — 3.6V Ni-MH Replacement Battery

This is a 3.6V, 600mAh Ni-MH rechargeable battery for the Phone Mate SL4 and SL5 cordless handsets. It slots directly into the handset battery compartment and restores talk and standby power. Voltage and cell count match the original pack.

• SL4 and SL5 compatibility: Both models share the same handset platform, battery bay dimensions, and 3.6V three-cell Ni-MH configuration. One battery fits both. No wiring or connector differences between the two.
• Bench tested on actual hardware: We cycled this pack through charge and discharge on a Ni-MH test rig. The cell voltage held within spec across the full discharge curve, and the base station accepted the charge handshake without error flags on repeated cycles.
• First-charge protocol for Ni-MH handsets: After installing, seat the handset in the base and leave it for a full 16 hours before first use. Ni-MH cells in cordless phones ship in a partially discharged state — the slow first charge allows each cell to reach balanced capacity. Skipping this step is the most common cause of short talk time on a new pack.

Base station showing no charge light on a fresh Ni-MH pack

Ni-MH batteries lose voltage during storage. If the pack sits in a warehouse long enough, its resting voltage can drop below the threshold the base station uses to detect a valid battery. The base sees the low voltage and withholds charge rather than risk a fault condition. Place the handset in the base anyway and leave it — most Phone Mate bases will begin a trickle charge after several minutes once the cells respond. If the charge light still does not appear after 30 minutes, remove the handset, wait 10 seconds, and reseat it to trigger a fresh detection cycle.

Range drops noticeably mid-call after fitting new battery

The SL4 handset's RF transmit circuit draws a short current spike every time it sends a signal burst to the base. A Ni-MH pack that has not been fully conditioned has higher internal resistance, which causes voltage to sag under that RF load. The base station interprets the weaker signal as distance and reduces link quality. Run three full charge-discharge cycles — charge to completion, use the handset until it prompts low battery, then recharge fully — and internal resistance will drop to rated levels. After conditioning, transmit voltage should hold above 3.2V under load.