Red and green flashing together usually means a charging error, not a dead battery

When your Milwaukee battery flashes red and green at the same time, the charger has detected a problem and stopped charging to protect the battery. This is not the same as a slow charge or a battery that needs time to wake up. The charger is telling you something is wrong with either the battery itself, the charger, or the connection between them.

The most common causes are a battery that has gotten too hot or too cold, a charger that is not making solid contact with the battery terminals, or a battery that has internal damage. You can usually fix this yourself in a few minutes by checking the connection and letting the battery cool down. If those steps do not work, the battery or charger may need to be replaced.

Key Takeaways

  • Red and green flashing together means the charger detected a fault and stopped the charge to protect the battery.
  • Clean the metal contacts on both the battery and charger with a dry cloth, because dirt or corrosion blocks the electrical connection.
  • Let a hot battery cool to room temperature before trying to charge it again, which usually takes 15 to 30 minutes.
  • If the flashing continues after cleaning and cooling, the battery or charger likely has internal damage and will need to be replaced.

Check the battery and charger contacts first

The metal terminals where the battery slides into the charger can get dirty, corroded, or misaligned. When the connection is not solid, the charger cannot read the battery properly and stops the charge. Look at the four metal contacts on the back of the battery and the four slots inside the charger where the battery sits.

If you see any dirt, dust, or a white or green crusty coating, that is corrosion. Use a dry cloth or a pencil eraser to gently rub each contact until it looks shiny again. Do not use water or cleaning liquid. After cleaning, slide the battery into the charger firmly until you hear or feel it click into place. Wait a few seconds and check whether the light has changed.

Let the battery cool down if it feels warm

Milwaukee chargers stop charging when a battery gets too hot, because heat damages the cells inside. If the battery feels warm to the touch, remove it from the charger and set it on a clean, dry surface away from direct sunlight or heat sources. Let it sit for 15 to 30 minutes until it feels cool.

Cold batteries also trigger the flashing red and green light. If you have been working outside in freezing weather or left the battery in a cold car, bring it indoors and let it warm up to room temperature before charging. Once the battery is at a normal temperature, put it back in the charger and check the light again.

Try a different charger if you have one available

If cleaning the contacts and letting the battery cool did not stop the flashing, the problem might be the charger itself rather than the battery. If you have access to another Milwaukee charger that fits the same battery size, try charging the battery with that charger. If the light turns solid red or solid green, your original charger has a fault and should be replaced.

If the battery still flashes red and green with a different charger, the battery itself has internal damage. This can happen if the battery has been dropped, exposed to water, or charged too many times. A damaged battery cannot be repaired and will need to be replaced.

Understand what other Milwaukee battery light colors mean

A solid red light means the battery is charging normally. The charger will turn the light off or switch it to green when the charge is complete, depending on your charger model.

A solid green light means the battery is fully charged and ready to use. You can remove it from the charger at any time.

Red and green flashing together is the fault code you are seeing now. It stops the charge to prevent damage.

A light that does not turn on at all usually means the charger is not plugged in, the outlet is not working, or the charger itself is broken. Try plugging the charger into a different outlet to rule out a bad outlet.

When to replace the battery or charger

If the red and green flashing continues after you have cleaned the contacts, let the battery cool, and tested with a different charger, one of these parts has failed. Milwaukee batteries typically last 300 to 500 full charge cycles before the cells wear out. If your battery is more than three or four years old and has been used regularly, it is probably at the end of its life.

Chargers fail less often than batteries, but they can be damaged by power surges, water exposure, or internal component failure. If a different battery charges normally in your charger, the battery is the problem. If your battery flashes red and green in multiple chargers, the battery is the problem. If only one charger shows the fault code, replace that charger.

How to prevent this problem in the future

Store your batteries in a cool, dry place between 50 and 80 degrees Fahrenheit. Do not leave them in a hot car, a freezing garage, or a damp basement. Keep the metal contacts clean by wiping them with a dry cloth every few months, especially if you work in dusty or wet conditions.

Avoid letting the battery fully drain before charging it. Lithium batteries like the ones in Milwaukee tools last longer if you charge them when they reach 20 percent capacity rather than waiting until they are completely dead. Do not overcharge — remove the battery from the charger as soon as the light turns green, rather than leaving it plugged in overnight.

Frequently Asked Questions

Can I use my Milwaukee battery in a different brand of charger?

No. Milwaukee batteries are designed to work only with Milwaukee chargers. The connection shape and electrical signals are different from other brands. Using the wrong charger can damage the battery or charger, or create a safety hazard.

Is it safe to use a battery that flashes red and green?

No. The charger is stopping the charge because it detected a fault. Using a battery with an internal fault can cause it to overheat, lose power suddenly during use, or fail to hold a charge. Stop using it until you have figured out whether the battery or charger is the problem.

How long does a Milwaukee battery take to charge?

Most Milwaukee batteries take 30 minutes to 2 hours depending on the battery size and charger model. Smaller batteries and faster chargers finish sooner. Check your charger manual for the exact time for your specific battery and charger combination.

What does it mean if the charger light never changes from red?

A solid red light that stays red for more than the normal charge time usually means the battery is not making good contact with the charger. Remove the battery, clean both sets of contacts with a dry cloth, and try again. If the light still does not change after 2 hours, the charger or battery may be faulty.

Can I charge a Milwaukee battery in the cold?

Milwaukee chargers will not charge a battery below 32 degrees Fahrenheit. If you need to charge in cold weather, bring the battery indoors and let it warm up first. Charging a cold battery can damage the cells permanently.