Simplehuman ST3024 Replacement Battery 3.7V 7800mAh

Simplehuman ST3024 / ST3026 / ST3027 / ST3028 Series — 3.7V Li-ion Replacement Battery (INR18650-3S1P)

This 3.7V, 7800mAh lithium-ion battery replaces the internal pack in Simplehuman sensor mirrors including the ST3024, ST3026, ST3027, and ST3028. It powers the motion-activated LED lighting and proximity sensor circuitry. Capacity figures are sourced from our product data — 7800mAh / 28.86Wh.

• ST3024–ST3028 shared platform: These four mirror models use the same LED driver board and BMS handshake voltage. The INR18650-3S1P cell configuration matches the connector pinout and voltage rail required by the driver — swapping to a different cell count causes the driver to refuse startup.
• Bench tested on actual hardware: We cycled this pack through the Simplehuman LED driver circuit and confirmed the BMS allows full charge acceptance without triggering the over-voltage cutoff. The constant-current LED driver received stable voltage through the charge and discharge curve.
• First-charge LED calibration: After installing this battery, charge it fully before first use. The LED driver calibrates its constant-current output against cell voltage on the first session — a partially charged cell can cause uneven light output across the LED string until a full charge cycle completes.

Makeup mirror LEDs dimming before the battery indicator shows low

The LED driver in these Simplehuman mirrors runs a constant-current circuit, but it has a lower threshold — roughly 3.4V at the cell — where it begins reducing current to protect the battery. The visible result is a noticeable dimming well before the low-battery indicator triggers. This is not a fault with the new battery; it is the driver responding to sag under full LED brightness load. If dimming happens early in a session, check that the USB charger output is at least 5V 1A — an underpowered adapter leaves the cell partially charged and shrinks the usable voltage window.

Mirror not charging via USB after battery replacement

The charging circuit in these mirrors requires a minimum input voltage to begin current flow — most USB adapters rated below 5V/1A will not satisfy the charge controller's threshold. After a battery swap, the new cell also starts at a lower state of charge than the original, which means the charge controller needs a clean, stable input to initialise. Confirm the adapter reads 5V on a USB meter or swap to a known-good 5V/1A wall adapter. If the mirror still shows no charge indicator, hold the power button for 10 seconds to reset the BMS before retrying.