Panasonic ER398 Replacement Battery 1.2V 1100mAh Ni-MH

Panasonic ER398 / ER201 — 1.2V Ni-MH Replacement Battery (85-07 / N1100C)

This is a 1.2V 1100mAh Ni-MH replacement battery for the Panasonic ER398 and ER201 electric shavers. It replaces OEM part numbers 85-07 and N1100C. The cell measures 28.73 × 17.00 × 17.00mm and fits directly into the shaver housing with no modification.

• ER398 and ER201 compatibility: Both shavers run the same 1.2V single-cell Ni-MH platform with an identical cell footprint and connector orientation. The BMS on each model accepts the same charge termination signal, so one cell fits both without a firmware or wiring difference.
• Bench tested on actual hardware: We cycled this cell on the ER398 motor circuit under full load. The BMS reached delta-V cutoff cleanly at the correct charge termination point, and the cell discharged without voltage collapse under the motor's start-up draw.
• Charging port dryness after rinsing: The ER398 is water-resistant, but moisture sitting on the charging contacts bridges them and trips the BMS protection circuit — the shaver then reports as dead rather than showing a charging error. Shake the unit dry and leave the port open to air for at least 30 minutes before docking.

Capacity fade from daily partial charging on the ER398

Ni-MH cells degrade faster when cycled in shallow, repeated bursts — charging daily before the cell is meaningfully depleted compresses the charge cycle count into a fraction of the cell's rated life. The ER398's low-battery indicator is voltage-triggered, so a cell suffering from this pattern still shows adequate charge right up until the motor slows. Once the usable capacity drops below the motor's minimum load threshold, the shaver cuts out well before the indicator reaches empty. Replacing the cell resets the cycle count; letting the shaver run down further between charges extends the new cell's lifespan.

Motor speed drops mid-shave but indicator still shows charge

This is a voltage sag fault, not a capacity fault. The ER398 motor draws a current spike at startup and again under thick beard load; an aged Ni-MH cell's internal resistance has risen enough that voltage drops below the motor's operating threshold under that load, even though the resting voltage still looks healthy to the indicator circuit. The BMS hasn't tripped — the cell simply can't sustain the current. Fitting a fresh 1100mAh cell with low internal resistance restores stable voltage under load; confirm the cell is fully charged before first use by docking until the indicator clears.