Shark 550R Replacement Battery 3.7V 190mAh Li-Polymer

Shark 550R — 3.7V Li-Polymer Replacement Battery (PL552025)

This 3.7V 190mAh Li-Polymer battery replaces the OEM cell in the Shark 550R flashlight. It fits the 550R's compact battery bay and reconnects directly to the LED driver board. Capacity matches the original PL552025 specification at 0.7Wh.

• 550R platform fit: The 550R uses a single-cell Li-Polymer pack with a fixed 3.7V nominal rail feeding the LED driver. The PL552025 footprint — 26.50 × 20.34 × 5.00mm — is what locks this cell to that chassis. Any deviation in thickness or length will prevent the housing from closing.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the bench and confirmed the BMS protection circuit trips correctly at the low-voltage cutoff threshold, preventing cell damage under full LED draw.
• Driver load tip for the 550R: The 550R's LED driver pulls current in short high-intensity bursts. Avoid leaving the flashlight switched on in a bag or case unintentionally — parasitic drain at the driver level will pull the cell below its recovery threshold faster than standby self-discharge alone.

Shark 550R dimming before the battery indicator drops

The 550R's LED driver includes brownout protection that steps output down before the battery indicator registers low. This happens because the driver monitors voltage at the board, not at the cell terminal. At roughly 3.4V cell voltage, the driver reduces current to the LED rather than risk an uncontrolled cutoff. If the light dims noticeably but the indicator still shows charge, the cell is approaching its lower usable voltage — recharge now rather than continuing to draw.

550R light cycling through modes on its own near end of charge

Spontaneous mode-cycling near the end of a charge cycle is a driver response to voltage instability, not a firmware fault. As the cell sags under load, the driver briefly loses the voltage headroom it needs to hold a stable mode, resets, and re-initialises — which reads to the user as mode switching. Switch to the lowest output mode to stop the cycling. Recharge the cell; full charge restores the voltage rail to the stable operating range above 3.7V.