About this replacement
Ember Mug 2 — 7.4V Li-ion Replacement Battery (INR18650 MH1-2S1P)
This is a 7.4V, 3500mAh Li-ion battery pack for the Ember Mug 2. It fits the 2S1P cell configuration the Mug 2 uses to power its heating element and temperature sensor. Install this when your mug no longer holds a charge or can't sustain its set temperature.
- Ember Mug 2 compatibility: The Mug 2 uses a 7.4V two-cell series pack with a dedicated BMS that monitors cell balance and temperature during heating cycles. This replacement matches that voltage rail and BMS handshake — the firmware won't activate the heater without the correct cell count and voltage signal.
- Bench tested on actual hardware: We ran this pack through full heat cycles on the Mug 2. The BMS held cell balance within spec under heater load, and the temperature sensor received a stable voltage throughout. No mid-cycle cutoffs occurred during testing.
- Post-install charge cycle: After fitting this battery, charge the mug to 100% before first use. The Mug 2 firmware runs a calibration pass from full charge — skipping this causes the temperature control loop to read thermostat targets inaccurately on the first few cycles.
Why the Mug 2 stops heating before reaching your set temperature
The Mug 2's heating element draws a sustained high current to reach and hold temperature. As a Li-ion pack ages, internal resistance climbs — under heater load, voltage sags below the threshold the BMS needs to keep the element active. The mug may show a full charge indicator but still cut heating short. A replacement pack with low internal resistance restores the sustained voltage the heater circuit requires.
Mug 2 not reconnecting to the Ember app after battery replacement
A complete power interruption — which a battery swap causes — clears the mug's active Bluetooth pairing state. The Ember app treats this as an unknown device rather than a known mug. Open the app, remove the mug from your device list, then hold the mug's button for five seconds to enter pairing mode. Re-add it as a new device to restore full app control.