About this replacement
Eufy Video Doorbell E340 — 3.7V Li-ion Replacement Battery (T8743)
This is a 3.7V, 6500mAh Li-ion replacement battery for the Eufy Video Doorbell E340. It matches the OEM T8743 part number and slots into the E340's battery bay. Dimensions are 77.00 × 40.20 × 21.50mm — confirm yours before ordering.
- E340 platform fit: The E340 runs a single-cell 3.7V architecture with a proprietary BMS handshake that monitors cell voltage and temperature before enabling the recording pipeline. This cell meets that voltage rail and communicates correctly with the doorbell's protection circuit.
- Bench tested on actual hardware: We cycled this cell through motion-triggered recording events and night vision activation. The BMS held cutoff thresholds correctly at both ends, with no false low-voltage shutdowns during combined IR LED and processor draw spikes.
- App registration after install: After fitting this battery, power cycle the doorbell once through the Eufy Security app. The firmware must re-register the new cell before motion event logs record correctly to cloud storage — skipping this step causes missed clips.
Camera going offline in the Eufy app after battery swap
Swapping the battery clears the doorbell's active firmware session token. The E340 drops off the app's device list because it treats a cold-boot power event as a new network session. Re-open the Eufy Security app, navigate to Device Settings, and trigger a manual reconnect. If the doorbell still shows offline, hold the sync button for five seconds to force a fresh pairing handshake at 3.7V standby state.
App reporting 0% or wrong battery percentage after fitting the T8743
The E340 uses a voltage-threshold indicator, not a fuel-gauge IC. It maps charge level to a set of fixed voltage steps — a new cell's resting voltage may not land cleanly on those steps until after one full charge cycle. Charge the doorbell to 100% via the USB-C port, then let it discharge through normal operation. After one complete cycle, the percentage display recalibrates to the cell's actual voltage curve.