DeWalt Battery Not Charging Red Light Flashing

Quick answer

• On DeWalt's 20V MAX chargers, a slow steady blink is normal charging and a solid red light means the pack is full. A flash that never completes usually means a temperature lockout or a contact problem, not a dead battery.
• Lithium-ion won't accept a charge below about 32°F (0°C) or when it's too hot. That's a built-in safety interlock, not a defect.
• A genuinely failed pack on a DCB107, DCB112, DCB113, DCB115, or DCB118 charger often shows no light at all, rather than a flash.
• Clean the contacts, let the pack reach room temperature, and test it against a known-good charger before you write it off.

Symptoms

You drop a 20V MAX pack on the charger and the red light flashes, but it never switches to the solid "ready" state. The pack stays at the same charge level, or won't run a tool for more than a few seconds. Sometimes the light flashes a quick double blink and stops. Sometimes there's no light at all and you assumed it was flashing.

What the light is telling you

DeWalt keeps the LED simple, so read it carefully:

• Slow, steady blink: the pack is charging. This is normal. Let it finish.
• Solid red: the pack is fully charged and ready.
• Yellow light (on chargers that have one): hot/cold delay. The charger is waiting for the pack to reach a safe temperature and will start on its own once it does.
• Quick double blink, then nothing: a low-voltage "wake-up" flag on a deeply discharged pack.
• No light with any pack inserted: the charger isn't getting power, or the charger itself has failed.

The key point people miss: on the DCB1xx chargers, a truly dead pack tends to show no light at all rather than a steady flash. So a persistent flash is more often a fixable condition than a death sentence.

Try this first: temperature

This is the number one cause, especially in summer or winter.

1. If the pack came out of a hot truck cab, a sun-baked job site, or off a tool you just ran hard, it's heat-soaked. Set it aside for 30 minutes to reach room temperature, then try again.
2. If it's been in a cold garage, Li-ion won't charge below roughly 32°F. Bring it indoors and let it warm up first. The charger will refuse it until then, and that's normal behavior.

Then work the connection

3. Pull the pack and reseat it firmly. You should feel it click home. A pack that's a hair short of fully seated reads as a fault.
4. Look at the rails and contacts on both the pack and the charger. Sawdust, grime, and metal filings bridge or block the terminals. Brush them out dry, or wipe with a little isopropyl alcohol and let it dry.

Isolate the charger from the battery

5. Put a known-good 20V MAX pack on the suspect charger. If the good pack charges fine, your charger is okay and the original battery is the problem. If the good pack also won't charge, the charger or the outlet is at fault.
6. Try the suspect pack on a different 20V MAX charger. Stick to 20V MAX gear here. DeWalt's 12V MAX is a separate system and won't help you diagnose this, and a 20V MAX pack belongs only on a 20V MAX charger.
7. Confirm the outlet works with another device, and check the charger cord for damage.

Reviving an over-discharged pack

If the pack was stored flat for months, its voltage may have dropped below the charger's wake threshold. Leave it on the charger for 20 to 30 minutes even if it looks unresponsive. The charger will sometimes trickle it back above the cutoff and then begin a normal charge. If it hasn't woken after half an hour, it probably won't.

When the pack is actually dead

Here's the line between a normal interlock and a real failure. A cold or dirty pack that won't charge isn't broken. But if a room-temperature pack with clean contacts still won't charge on a charger you've confirmed works, a cell or the pack's protection board has likely failed. At that point it's a replacement, not a repair, since the cells are sealed and not user-serviceable.

Check the date code stamped on the battery before you buy a new one. DeWalt's 20V MAX batteries carry a three-year limited warranty, and a pack that failed inside that window is a free replacement through DeWalt service rather than money out of your pocket.