Streamlight Strion HPL 3.7V Replacement Battery 74031

Streamlight Strion HPL Flashlight — 3.7V Li-ion Replacement Battery (74031)

This is a 3.7V 3500mAh Li-ion replacement battery for the Streamlight Strion HPL and Strion LED series flashlights. It fits a wide range of Strion variants including the Strion DS HL and ProTac HL USB. The OEM part numbers covered include 74031, 74032, 74175, and over thirty additional Streamlight references.

• Strion and ProTac platform fit: These models share the same cylindrical cell format, 3.7V nominal voltage rail, and proprietary charging contacts. The BMS handshake across this platform is consistent, so one cell format covers the full lineup without modification.
• Bench tested on actual hardware: We ran this cell through full charge and discharge cycles on a Strion HPL body. The BMS engaged cleanly at both ends — no false low-battery cutoff on draw, and charge termination landed within spec at the top of the cycle.
• Turbo mode thermal load: The Strion HPL driver pulls significantly higher current in turbo mode than in standard. Let the cell rest for a few minutes after sustained turbo use before recharging — heat carried into the charger shortens cell life faster than cycle count alone.

Strion HPL driver stepping down output before the indicator shows low

The Strion HPL's driver has brownout protection built in. When cell voltage drops under high current draw, the driver steps output down before the low-battery indicator triggers — so the light dims visibly while the indicator still reads normal. This is the driver protecting itself, not a faulty cell. It happens earlier with an aged cell because internal resistance is higher, causing a larger voltage sag under load. A fresh 3500mAh cell at full charge will push the step-down point later in the discharge curve.

Cell draining to zero during storage — flashlight dead on first use

Li-ion cells self-discharge slowly in storage, and if the cell drops below the BMS deep-discharge threshold — typically around 2.5V — the protection circuit opens and the charger sees a dead load. The Streamlight charger may show no charge activity or a fault light. To recover, place the cell on a Li-ion charger capable of trickle or pre-charge mode at 0.1C until voltage climbs above 3.0V, then resume normal charging. Avoid storing the flashlight with a depleted cell for more than a few weeks.