Streamlight UltraStinger LED 6V Replacement Battery 3000mAh

Streamlight UltraStinger LED / SL-20XP-LED Series — 6V 3000mAh Ni-MH Replacement Battery (77375)

This is a 6V, 3000mAh Ni-MH replacement battery for the Streamlight UltraStinger LED flashlight and SL-20XP-LED, SL-20L, and SL-20LP series. OEM part number 77375 is the reference match for this battery pack. It fits the stick-format battery bay used across these Streamlight tactical flashlights.

• UltraStinger LED and SL-20 series compatibility: These models share the same 6V Ni-MH battery bay, connector orientation, and charge-management circuit. The charger communicates with the battery through delta-V detection — cell chemistry must match Ni-MH exactly or the charger will not terminate correctly.
• Bench tested on actual hardware: We cycled this battery through the OEM Streamlight charger and confirmed the delta-V cutoff triggered cleanly at full charge. The BMS showed no false termination during the first three charge cycles, which is where Ni-MH cells are most prone to early cutoff.
• Ni-MH cycle care for high-draw flashlights: The UltraStinger LED draws high current at full output — do not leave the battery sitting in a discharged state after use. Ni-MH cells that sit fully depleted for more than a few days develop voltage depression that causes the charger to reject the pack as faulty.

Why the UltraStinger LED steps down output before the low-battery indicator triggers

The UltraStinger LED driver monitors cell voltage continuously. When voltage drops below the driver's brownout threshold — typically around 4.8V on a 6V Ni-MH pack — it steps output down to protect the LEDs from under-voltage flicker. This happens before the battery indicator registers low because the indicator trips at a different threshold than the driver protection circuit. The result is a noticeable dimming that looks like a faulty battery but is actually normal end-of-discharge behaviour. Recharge the pack promptly when dimming begins.

Charger rejecting the new battery on first install

Fresh Ni-MH cells often sit at a resting voltage that confuses the delta-V charger into treating the pack as already full or as a fault condition. This shows up as the charger light staying green immediately or blinking an error on first connection. The fix is to run the flashlight on low mode for 10–15 minutes to pull the cell voltage down slightly, then place it on charge — the charger will now see a genuine voltage rise and complete a proper charge cycle. If the charger still rejects it, check that resting voltage is at or above 5.0V before attempting to charge.