Milwaukee 48-11-2121 Flashlight Replacement Battery 3.6V 3000mAh

Milwaukee 2112-21 / 2114-21 Series — 3.6V Li-ion Replacement Battery (48-11-2121)

This is a 3.6V Li-ion battery rated at 3000mAh (10.8Wh), built to fit the Milwaukee 2112-21, 2114-21, 2128-21, and 2163-21 work light flashlights. It replaces OEM part numbers 48-11-2121 and 48-11-2131. When the original cell degrades and the light no longer holds a charge, this unit restores full output without replacing the torch.

• Cross-model fit — 2112-21 through 2163-21: These Milwaukee work lights share the same single-cell 3.6V Li-ion form factor, connector orientation, and BMS communication protocol. One battery covers all listed models.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the 2112-21 platform. The BMS handshake completed cleanly, protection thresholds triggered at the correct low-voltage cutoff, and the driver registered full charge without error flags.
• Single-cell replacement tip: This flashlight runs on one cell — so there is no cell-matching concern. However, do not partially discharge the new battery before first use. These Milwaukee lights run a compact driver that can interpret a low starting voltage as a fault and step down output immediately on first power-on.

Why the 2112-21 output drops before the low-battery indicator triggers

The Milwaukee work light driver uses brownout protection to step down LED output before the cell actually hits the low-voltage cutoff. This means you will see dimming while the indicator still shows charge remaining. It is intentional — the driver preserves a voltage buffer to allow safe shutdown rather than a hard cutoff. If the light dims early and recovers after a short rest, the cell is near end-of-charge and the protective step-down is working as intended.

Flashlight powers on briefly then shuts off — what is actually happening

This usually means the cell voltage has dropped below the BMS re-enable threshold after a period of storage or deep discharge. The BMS trips the protection circuit, and the light cannot draw enough current to stay on. Placing the battery on charge immediately after this symptom appears is the fix — most BMS circuits on this platform re-initialise once they detect a valid charger voltage above 3.0V. If the charger does not recognise the pack, hold it on charge for 10–15 minutes to allow the BMS to reset before the charge LED activates.