Streamlight SL-15X Replacement Battery 6V 2000mAh

Streamlight SL-15X / SL-20XP — 6V Ni-MH Replacement Battery (25170)

This is a 6V, 2000mAh Ni-MH replacement battery for the Streamlight SL-15X and SL-20XP rechargeable flashlights. It uses OEM part number 25170 and slots directly into the flashlight's battery compartment. At 12Wh, it matches the original cell pack specification these lights were built around.

• SL-15X and SL-20XP platform fit: Both models share the same cylindrical battery form factor, 6V nominal voltage rail, and charge circuit handshake — one replacement battery covers the full SL-X series using part 25170.
• Bench tested on actual hardware: We ran this pack through charge cycles on the SL-20XP cradle. The BMS accepted charge without fault codes, held voltage through high-draw bursts, and showed no thermal event at termination.
• Multi-cell pack handling: This is a sealed multi-cell Ni-MH pack. Never mix this new pack with a partially used original — if you run two separate packs in rotation, label them and cycle each pack as a unit. Mixing cells at different states of health forces the weaker cell to over-discharge under high-current draw.

Flashlight driver stepping down output before the battery looks empty

The SL-15X uses a constant-current driver that monitors pack voltage. When pack voltage sags under high-current draw — even if the battery still holds a nominal charge — the driver reduces output to protect the cells. This is intentional brownout protection, not a faulty battery. On an aged Ni-MH pack, internal resistance rises and voltage sag happens earlier in the discharge curve. A fresh pack with lower internal resistance holds voltage longer under the same draw, so the driver steps down less frequently and output stays consistent through more of the cycle.

Flashlight cycling between modes or flickering at end of charge

When pack voltage drops close to the driver's brownout threshold, the light can oscillate — briefly stepping down, recovering slightly, then stepping down again. This creates a flickering or mode-cycling effect near the end of the discharge. It is not a switch fault or driver failure. Switching to a lower output mode reduces current draw enough to keep voltage above the cutoff threshold and stabilises output. If this happens mid-session on a recently charged pack, check that the pack reached full charge — a Ni-MH cell terminated early can sit at 6.0V open-circuit but sag to 5.4V or below under load within minutes.