Sharp TQ-G 400 Replacement Battery 6V 650mAh Ni-MH

Sharp TQ-G 400 / TQ-G 450 — 6V Ni-MH Replacement Battery

This is a 6V 650mAh (3.9Wh) Ni-MH replacement battery for the Sharp TQ-G 400 and TQ-G 450 handheld cordless telephones. It slots into the battery compartment and restores full charge capacity when the original cell has degraded beyond useful service. Voltage and connector match the original Sharp specification.

• TQ-G 400 and TQ-G 450 fit: Both models run the same 6V battery rail and share the same physical housing and connector orientation, so one cell covers both handsets without modification.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the bench, confirming the Ni-MH chemistry accepted a full charge without thermal runaway and held voltage across the full discharge curve.
• Ni-MH conditioning after installation: Ni-MH cells in cordless phones are vulnerable to voltage depression if topped up repeatedly from shallow states. Run the handset down to cutoff and charge it fully for the first two cycles after fitting — this prevents early capacity loss caused by the memory effect common to Ni-MH chemistry.

Why the TQ-G 400 stops holding a charge after shallow cycling

Ni-MH cells in cordless handsets are prone to voltage depression — a condition where repeated partial charges train the cell to deliver less voltage over time. The TQ-G 400 charges whenever it sits in the cradle, which means most users never fully discharge the pack. Over months, the cell's effective capacity shrinks even though it appears to charge normally. Two full discharge-to-cutoff cycles after fitting a new cell resets this pattern and lets the cell establish its true capacity baseline.

Handset shows full charge on the indicator but cuts out during a call

This happens when the cell voltage collapses under the current draw of an active call before the charge indicator has caught up. The TQ-G 400 charge indicator reads resting voltage, not load voltage — so a partially degraded or freshly fitted cell can show full bars at rest but drop below the cutoff threshold the moment the handset transmits. The fix is to complete two full discharge-charge cycles so the cell's loaded voltage profile stabilises. After conditioning, the indicator and actual capacity align closely enough for normal use.