Coast FL60R Replacement Battery 3.7V 1100mAh Li-Ion

Coast FL60R / FL75R / FL85R Series — 3.7V Li-ion Replacement Battery

This 3.7V 1100mAh Li-ion cell replaces the internal rechargeable battery in the Coast FL60R, FL75, FL75R, and FL85R flashlights. These lights use a single flat-format Li-ion cell measuring 44.90 × 31.10 × 9.00mm. Swap this in when the original cell no longer holds charge or charges incompletely.

• FL60R / FL75 / FL75R / FL85R platform fit: These models share the same cell bay dimensions and 3.7V driver voltage rail. The cell connects directly to the driver board, which regulates output across all brightness modes from a single cell input.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the FL60R driver. The BMS held cutoff at the correct low-voltage threshold and accepted a full charge without tripping protection prematurely.
• Driver compatibility tip: Coast's FL-series driver reads cell voltage directly to manage mode stepping. If the replacement cell sits at storage voltage (around 3.6V) when first installed, the driver may start in a reduced output mode — charge fully before your first use after installation to let the driver calibrate to peak cell voltage.

Why the FL60R steps down output before the indicator shows low

Coast's FL-series driver uses brownout protection to step the output down before the battery reaches a hard cutoff. This protects the cell from deep discharge but means the light gets noticeably dimmer while the indicator still shows charge remaining. The driver starts reducing current draw when cell voltage drops below roughly 3.4V under load. That threshold is intentional — running the cell lower risks capacity loss over repeated cycles.

Flashlight cycling between modes or flickering at end of charge

If the FL60R flickers or toggles between brightness levels on its own near the end of a charge, the driver is hitting its brownout floor repeatedly under load. This happens when the cell voltage sags under draw, recovers briefly, then sags again. Switching to a lower output mode stops the cycling and draws less current, keeping voltage above the cutoff threshold. If it happens on a freshly charged cell, check that the cell contacts are clean and making full contact — resistance at the terminals causes voltage sag before the cell itself is depleted.