Theradome LH40 Replacement Battery 3.7V 2600mAh Li-ion

Theradome LH40 / LH80 / LH80 Pro — 3.7V Li-ion Replacement Battery (INR18650-1S1P)

This 3.7V, 2600mAh Li-ion cell replaces the internal battery in the Theradome LH40, LH80, and LH80 Pro laser hair growth helmets. The original INR18650-1S1P format is a standard 18650 single-cell configuration running a 1S1P arrangement. Capacity and voltage match the OEM spec exactly — 9.62Wh total.

• LH40, LH80, and LH80 Pro compatibility: All three Theradome helmets share the same single-cell 18650 battery bay, voltage rail, and BMS handshake protocol. One cell format covers the entire current Theradome lineup without modification.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on an LH80 unit. The onboard BMS accepted the cell without error, balanced the charge curve correctly, and held voltage within spec across a full session.
• Port moisture before charging: After using the helmet — particularly if worn during a warm environment or scalp perspiration is a factor — let the charging port air out for at least two minutes before connecting. Residual moisture at the contacts can trigger a BMS protection fault that registers as a dead battery rather than a charge error.

Battery fade from daily top-up charging on the Theradome

Many Theradome users charge after every session rather than waiting for the battery to drop meaningfully. Li-ion cells degrade faster when cycled repeatedly in the upper 80–100% range without full discharge. This compresses the usable capacity over time and causes the charge indicator to drift — showing full when actual stored energy is well below spec. To slow this, allow the cell to discharge to around 3.2–3.3V before reconnecting the charger.

Helmet powers on but laser array cuts out mid-session

This is a voltage sag symptom, not a controller fault. When the 18650 cell ages, its internal resistance rises. Under the combined load of 80 laser diodes, the voltage drops sharply during peak draw — enough to trip the BMS low-voltage cutoff even if the indicator still shows charge remaining. A new cell at full 3.7V nominal resolves the sag. If the issue persists with a fresh cell, check that the battery contacts inside the helmet are clean and making firm contact.