Philips 238 Replacement Battery 3.6V 650mAh Ni-MH

Philips 238 / Fisio 310–312 Series — 3.6V Ni-MH Replacement Battery

This is a 3.6V, 650mAh Ni-MH replacement battery for the Philips 238 handset and the Fisio 310, 311, and 312 series. It fits the original battery bay and connects directly to the charge circuit. Voltage and chemistry match the OEM specification exactly.

• Philips 238 and Fisio family compatibility: These models share the same 3.6V single-cell Ni-MH voltage rail and the same physical connector footprint. The charge IC on each device expects a Ni-MH cell — swapping to Li-ion would over-charge and damage the circuit. This cell keeps the chemistry correct.
• Bench tested on actual hardware: We cycled this cell through three full charge-discharge passes on the Philips charge circuit. The BMS accepted the cell without fault flags, and terminal voltage held within the expected 1.2V per cell window across the discharge curve.
• Ni-MH conditioning on first install: On first use, run two complete discharge-to-charge cycles before trusting the battery indicator. Ni-MH cells have a memory effect that affects how the phone's fuel gauge reads state-of-charge on a fresh, unconditioned cell.

Why the Philips 238 reports wrong battery percentage after a cell swap

The fuel gauge IC on the Philips 238 stores a discharge curve calibrated to the old cell. When a new Ni-MH cell goes in, the IC doesn't immediately know the new cell's actual capacity or voltage profile. It maps percentage against the old curve, so the reading drifts — often showing full for too long, then dropping fast. Running two full discharge-charge cycles forces the IC to re-learn the new cell's curve and corrects the percentage display.

Sudden shutdown at 20–30% on the replacement cell

A fresh Ni-MH cell has higher internal impedance than a well-cycled one. Under screen or call load, the voltage sags below the phone's low-voltage cutoff even though the fuel gauge still shows charge remaining. The device interprets the sag as a dead cell and shuts down. After two full conditioning cycles, internal impedance drops and the cell can hold voltage under load — the premature shutdowns stop. If the problem persists past three cycles, check that the cell contacts are fully seated and clean of oxidation.