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Power tool charger lights flashing: what it means

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In short

Flashing charger lights usually mean one of three things: the battery is too hot or too cold to charge yet, the charger cannot charge the pack because of dirty contacts or a fault, or the pack is deeply discharged or damaged. Let the pack reach room temperature, clean the contacts and try another battery. The exact meaning of each pattern is printed on most chargers and in the manual.

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A charger that blinks instead of charging is one of the commonest cordless tool problems. Every brand uses its own light patterns, and they change between charger models, so the label on the charger and the manual are the final word. This guide explains the common meanings, the safe checks you can do and when a battery should be retired.

Read the label on your charger

Most DeWalt, Makita, Milwaukee and Bosch chargers have a small chart on the case or in the manual showing what each light pattern means. Look there first. The general patterns below are common across brands but are not universal, so use them as a guide rather than a diagnosis.

What you seeCommon meaningWhat to try
Steady red or charging lightCharging in progressWait
Steady greenFully chargedRemove and use
Light on but waiting, or a separate symbolHot or cold pack delayLet the pack reach room temperature
Fast flashing or alternating coloursPack cannot be charged, fault or poor contactClean contacts, reseat, try another pack
No lightsNo mains power or charger faultCheck socket and fuse
Common meanings, check your charger's label

Hot and cold pack delay

Lithium-ion cells should not be charged when very hot or below freezing, so chargers pause until the pack is within a safe range. A pack straight off a hard working saw, or one brought in from a cold van or shed, often triggers this. The charger usually starts automatically once the temperature is right. Some chargers have a fan that cools the pack.

Do not try to speed things up with a heater or freezer. Leave the pack at room temperature. See how to store batteries in a cold shed or van.

Faulty pack or poor contact

If the charger flashes a fault pattern, remove the battery and check the terminals on both the pack and the charger for dust, debris or damage. Wipe them with a dry cloth. Reseat the pack firmly. Try another battery: if it charges normally, the first pack is the problem; if neither charges, the charger may be faulty.

Makita's DC18RC charger, for example, is widely documented as alternating red and green when a pack cannot be charged. DeWalt and Milwaukee use their own patterns for a problem pack or a hot or cold delay. Check your manual for your exact model.

  1. 1

    Unplug the charger and remove the battery.

  2. 2

    Inspect and wipe both sets of contacts.

  3. 3

    Let the pack reach room temperature.

  4. 4

    Plug back in and reseat the battery.

  5. 5

    Try a second battery and, if possible, a second charger.

Deeply discharged packs

A lithium pack left flat for months can fall below the voltage at which the charger will accept it. Some chargers try a gentle recovery charge; others show a fault. Do not try to force charge a pack with another device or jump start it from another battery, which can be dangerous.

If the official charger will not accept the pack after it has warmed to room temperature, it is likely at the end of its life.

When to retire a battery

Stop using any pack that is swollen, cracked, leaking, smells, gets very hot on the charger or has been dropped hard and now behaves oddly. Lithium cells can fail dangerously. Tape the terminals and take it to a battery recycling point; many tool retailers and council sites accept them.

Buy replacement packs from authorised sellers. Cheap copies may lack protection circuits; see how to spot fake Makita and DeWalt tools.

Getting the most from your batteries

Charge packs at room temperature, avoid leaving them in hot cars, and store them part charged if you will not use them for a while. Larger packs run cooler under heavy loads. If you are buying a kit, compare the battery sizes in our combi drill kit guide and twin pack guide.

Note:Never open, puncture or repair a lithium battery pack. Charge on a hard, non flammable surface away from anything that could catch fire, and do not leave packs charging unattended for long periods. Follow the maker's manual.

Frequently asked questions

Why does my DeWalt charger flash red? On many DeWalt chargers a fast flashing red light indicates a problem pack or charger, while other patterns show a hot or cold delay. Check the chart on your charger.

My Makita charger flashes red and green. Is the battery dead? It means the charger cannot charge the pack, which can be a fault or poor contact. Clean the contacts, try again at room temperature, then try another pack.

Can I leave batteries on the charger? Modern chargers stop when full, but it is good practice to remove packs once charged and not to leave them charging unattended for long periods.

Can a dead battery be revived? Sometimes a cold or poorly seated pack recovers. A pack the official charger rejects at room temperature should be recycled.

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