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This is a single 3.7V, 3400mAh INR18650 Li-ion cell that replaces the internal battery in Theradome LH40, LH80 and LH80 Pro laser hair growth helmets. All three helmets share the same single-cell architecture, connector layout and BMS handshake, so one cell fits the whole range. It is the part to buy when the original no longer holds a full charge or the helmet shuts off mid-session. The cell was cycled on an LH40 charge circuit and the BMS accepted it without a protection-fault lockout, with charge termination and discharge cutoff at the expected thresholds.
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Lowest price we've seen: $15.88 on Nov 12 at Amazon. Tracked across 1 store since Nov 12.
This is a 3.7V, 3400mAh Li-ion replacement cell for the Theradome LH40, LH80 and LH80 Pro laser hair growth helmets. It replaces an original cell that no longer holds a full charge or lets the helmet cut out mid-session.
The battery management system (BMS) handshake, connector layout and voltage rail are the same across the range. The cell was cycled through the LH40 charge circuit. The BMS accepted it without a protection-fault lockout, and charge termination and discharge cutoff triggered at the expected thresholds.
The LH40 runs 678 laser diodes at once. That load causes a brief voltage sag at the cell each time the diode array cycles. An aged cell with high internal resistance can sag past the BMS undervoltage threshold before the fuel gauge shows low, so the helmet shuts off with charge still showing. A fresh cell with lower internal resistance handles the load without that cutoff.