Simplehuman ST3004 Cosmetic Mirror Replacement Battery 3.8V 2600mAh

Simplehuman ST3010 5" Sensor Makeup Mirror — 3.8V Li-Polymer Replacement Battery (ST3004)

This 3.8V, 2600mAh lithium-polymer cell replaces the original ST3004 battery in the Simplehuman ST3010 5" Sensor Makeup Mirror. It powers the mirror's LED lighting array and motion-detection sensor circuitry. Capacity figures come from the product data — 9.88Wh.

• ST3010 and ST3004 mirror compatibility: Both the ST3010 and ST3004 cosmetic mirror variants share the same battery format, connector pinout, and 3.8V nominal cell voltage. The LED driver circuit and sensor module draw from a single cell, so the replacement cell must match voltage exactly — any deviation trips the protection circuit and the mirror won't power on.
• Bench tested on actual hardware: We cycled this cell through the ST3010's LED driver under full-brightness load and confirmed the BMS held stable output voltage across the draw curve. The protection circuit engaged correctly at the low-voltage cutoff threshold with no false trips during normal LED operation.
• First-charge calibration on this mirror: After fitting the new cell, charge the mirror fully before first use. The ST3010's LED driver calibrates its constant-current output against cell voltage on the initial charge cycle. Installing and using the mirror on a partial charge can cause uneven light output across the LED ring on that first session.

Why the ST3010's LEDs dim before the battery indicator drops

The ST3010 uses a constant-current LED driver, but that driver begins reducing current as cell voltage sags under load — before the battery indicator registers low. This happens because the indicator reads resting voltage, not load voltage. Under full-brightness draw, actual cell voltage can drop 0.2–0.3V below resting voltage, pushing the driver into current-reduction mode early. Replacing a degraded cell restores the voltage headroom the driver needs to hold full current output.

Mirror not charging via USB after a battery swap

The ST3010's USB charging circuit has a minimum input voltage requirement — a low-output USB port or a long, thin cable with high resistance can drop below the threshold, and the mirror simply won't register as charging. If the indicator light doesn't come on within 30 seconds of plugging in, try a different adapter rated at 5V/1A or above. Also confirm the battery connector is fully seated — a half-engaged connector breaks the charge path before it reaches the cell. Check the adapter output first, then reseat the connector.