About this replacement
Hairmax Prima 7 / Prima 9 — 3.7V Li-Polymer Replacement Battery (14L10)
This is the 3.7V, 1100mAh lithium-polymer battery for the Hairmax Prima 7, Prima 9, and PR7-V01 low-level laser therapy combs. It replaces OEM part number 14L10 when the original cell has degraded from repeated charge cycles. Capacity figures are taken directly from the product specification — 4.07Wh at 3.7V nominal.
- Prima 7, Prima 9, and PR7-V01 compatibility: All three models share the same battery bay dimensions (49.60 × 30.00 × 8.00mm), 3.7V nominal rail, and connector configuration. The BMS in each unit reads the same charge profile, so a single cell covers the full variant range without any wiring modification.
- Bench tested on actual hardware: We cycled this cell through charge and discharge on the Prima platform and confirmed the BMS accepted the cell, balanced correctly at 4.2V full charge, and engaged the protection circuit at the expected low-voltage cutoff without triggering a fault state.
- Charging port care after use near the scalp: Scalp oils and product residue transfer to the charging port during regular use. Wipe the port contacts with a dry cloth before docking — residue on the contacts can cause an intermittent connection the device reads as a BMS protection fault rather than a dirty contact.
Battery fade from daily top-up charging on the Prima 7
The Prima 7 is typically used in short sessions and then docked immediately. Frequent shallow charges — topping up from 60–80% rather than completing a full cycle — cause the cell's charge gauge to drift over time. The device starts reporting full charge earlier than the actual cell state. Capacity appears to drop suddenly, but the issue is cumulative gauge drift, not sudden cell failure. Running the battery from full down to the low-voltage cutoff once every few weeks resets the gauge alignment and restores accurate capacity reporting.
Prima 7 shows no charge after moisture exposure at the port
Moisture bridging the charging contacts trips the BMS protection circuit, which shuts down charging as a safety response — the device behaves exactly like a dead battery. The charge indicator shows nothing and the unit will not power on. Let the port dry completely at room temperature for at least two hours before attempting to reconnect. Once dry, reconnect the charger and confirm the charge LED activates within 30 seconds; if it does not, check the port contacts are clean and seated at 0V resistance before assuming cell failure.