The Lithium "Time-Bomb": Battery Chemistry in the HMM1

The Livenpace HMM1 weighs a mere 1.23 ounces. While this makes it comfortable to wear, it imposes a severe constraint on the energy storage system. The lithium-ion cell inside is likely in the range of 100-200mAh.

While the spec sheet claims 24-hour continuous recording, the physics of small lithium cells introduces a specific failure mode that plagues occasional-use devices: Deep Discharge Lockout.

The Storage Hazard

Many users buy an ECG monitor, use it for a few days to check a symptom, and then put it in a drawer for six months. This is a death sentence for the HMM1.

Lithium-ion batteries self-discharge over time. Small cells discharge proportionally faster due to the power draw of the Battery Management System (BMS) itself. If the cell voltage drops below a critical threshold (typically 2.5V), the BMS enters a “Protection Mode” to prevent chemical instability (dendrite growth) that could cause a fire upon recharging.

The “Bricked” Device Phenomenon

Once in Protection Mode, the device will appear dead. Connecting it to a charger (as shown in the Livenpace diagram) may not wake it up because the charging circuit refuses to apply current to a “unsafe” cell.

Users attempting to revive a dormant HMM1 often interpret this as a manufacturing defect. In reality, it is a characteristic of the chemistry. To mitigate this, users must treat the device like a living organism: it needs to be “fed” (charged) to 50-60% every few months, even if not in use.

The Charging Logic

The LED indicator turns orange during charge and green when full. However, if the device has been deeply discharged, the LED may not light up at all for the first 30 minutes of charging (the “Trickle Charge” recovery phase). Users often unplug it after 5 minutes, thinking it’s broken, effectively dooming the recovery process.