Check the fuel gauge on the battery pack itself. Press the button next to the LED lights.
Fix:
- Press the battery fuel gauge button. One to four LEDs will illuminate.
- Four solid LEDs means 76-100% charge.
- Three LEDs means 51-75%.
- Two LEDs means 26-50%.
- One LED means up to 25%. One flashing LED means critically low.
If that didn't work and no LEDs light at all, the battery is either completely dead or defective. Insert it into the M18 Rapid Charger (48-59-1808). A fully charged battery should show four solid LEDs.
Heads up: New batteries arrive with a minimal charge. You must charge them fully before first use.