Philips FIZFO-311 Replacement Battery 3.6V 750mAh

Philips FIZFO-311 / 312 / 310 / 610 — 3.6V Ni-MH Replacement Battery

This is a 3.6V, 750mAh Ni-MH replacement battery for the Philips FIZFO-311, 312, 310, and 610 mobile handsets. It slots into the original battery bay and restores power to the phone's core functions — calls, messaging, and basic applications. Capacity is 2.7Wh, matching the original cell specification.

• FIZFO-310 / 311 / 312 / 610 compatibility: These four models share the same 3.6V single-cell Ni-MH form factor, connector pinout, and charge termination logic. The BMS on each handset uses negative delta-V detection to end charge, which this cell chemistry supports natively.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the FIZFO platform. The BMS accepted the cell without fault codes, charge termination triggered correctly via negative delta-V, and voltage held stable under steady call-state load.
• Fuel gauge recalibration on first cycle: On first use after installation, disable fast charging if the option is present, then run one complete discharge-to-charge cycle. This lets the fuel gauge IC map the new cell's discharge curve before reporting percentage — skipping this step causes erratic readings early on.

Sudden shutdown at 20–30% on the FIZFO after a cell swap

Ni-MH cells have a steeper voltage drop-off curve than Li-ion, and the FIZFO fuel gauge IC may still be calibrated to the old cell's curve after a swap. Under load — an active call or screen-on state — the new cell's voltage dips faster than the gauge predicts, and the phone shuts off before the displayed percentage hits zero. This is not a faulty cell; it is the fuel gauge acting on stale data. One full discharge-charge cycle resets the coulomb counter and aligns the percentage display to the actual cell behaviour. After that cycle, shutdowns at 20–30% should stop.

Phone warm near the battery compartment during first charge

A new Ni-MH cell has higher internal impedance than a broken-in cell. The charge IC pushes current into that resistance, and some of it converts to heat rather than stored charge — this is normal on the first one or two cycles. If the handset feels warm to touch near the battery bay but not hot enough to be uncomfortable, let the charge complete and cycle the battery once more. Warmth should reduce significantly after the second full charge. If the case becomes too hot to hold, remove the battery and check the cell seating in the bay contacts.