About this replacement
Panasonic ES-RT30 / ES-SA40 Series — 1.2V Ni-MH Replacement Battery (WES7038L2506)
This is a 1.2V, 2000mAh Ni-MH replacement battery for Panasonic cordless electric shavers. It fits the ES-RT30, ES-RT40, ES-SA40, ES3042, and over 100 additional Panasonic shaver models. Swap it when the original cell degrades and the shaver cuts out before the indicator reaches empty.
- Cross-model fit — RT30, RT40, SA40, ES3042: These models share the same cell housing diameter (14.1mm), connector orientation, and BMS voltage thresholds. The same 1.2V Ni-MH cell works across all of them without wiring changes.
- Bench tested on actual hardware: We ran this cell through full charge-discharge cycles on the ES-RT30 platform. The BMS accepted the cell without fault codes, and charge termination triggered correctly at capacity.
- Charging port care after wet shaving: For waterproof models, dry the charging port completely before docking. Moisture bridging the charging contacts triggers a BMS protection trip — the device reports a dead battery, not a charging error.
Capacity fade from daily partial cycling on Panasonic shavers
Ni-MH cells in shavers degrade faster when partially discharged and topped up every day. The shaver's charge indicator calibrates against voltage curves, not true capacity. After months of shallow cycling, the cell's actual capacity shrinks but the indicator still reads full — until the motor load exposes the gap. A full discharge down to BMS cutoff followed by a full charge resets the voltage curve alignment and slows further drift.
Motor speed dropping mid-shave before the low battery indicator lights
The shaver motor draws a short current spike each time the cutter head engages dense stubble. A degraded Ni-MH cell can't sustain voltage under that load, so it sags below the motor's operating threshold before the BMS formally flags low battery. The indicator measures resting voltage, not loaded voltage — so the light stays off while performance drops. A fresh cell with full capacity holds voltage above 1.0V under motor load, which stops the speed drop entirely.