Eufy E330 Replacement Battery 3.7V 8800mAh T8520S

Eufy E330 / S330 Series — 3.7V Li-ion Replacement Battery (T8520S)

This is a 3.7V, 8800mAh (32.56Wh) lithium-ion battery for Eufy wireless security cameras using OEM part number T8520S. It fits the E330, S230 3-in-1 Video Smart Lock, S330, and S330 eufyCam, among other compatible models. Swap it in when the original cell no longer holds enough charge to sustain continuous recording and motion detection.

• E330 and S330 platform compatibility: These models share the same battery housing, connector orientation, and BMS voltage thresholds — 3.7V nominal with cutoff at the same low-voltage floor. One cell fits across the entire platform without wiring or hardware modification.
• Bench tested on actual hardware: We cycled this cell through simulated motion-trigger events, monitoring BMS behaviour at both the IR LED activation spike and the WiFi reconnect draw. The BMS held stable across both high-current moments without triggering a false cutoff.
• First-install firmware registration: After fitting the new cell, power cycle the camera once through the Eufy app. The camera's firmware must re-register the battery before motion events log correctly to cloud storage — skipping this step can cause missed clips despite the battery reading as charged.

App showing 0% or wrong percentage after installing this battery

Eufy cameras use a voltage-threshold indicator, not a fuel gauge IC. When a new cell goes in, the camera reads an unfamiliar voltage curve and maps it incorrectly until calibrated. One full charge-and-discharge cycle resets the thresholds. After that cycle, the app percentage should track the actual cell state accurately from around 4.2V full down to the 3.0V cutoff floor.

Recording stops mid-clip on weak WiFi signal

When the camera loses WiFi and immediately retries, the reconnect handshake pulls a short but sharp current spike. On a degraded original battery, that spike can cross the BMS overcurrent threshold and trigger a cutoff mid-recording. This replacement cell's higher internal headroom keeps the voltage from sagging below the trip point during that event. If clips still cut short, check that the camera sits within reliable WiFi range — move the access point or add a mesh node closer to the camera.