Why is my Milwaukee charger blinking red and green?
A Milwaukee charger blinking red and green usually means the charger has detected a fault condition with the battery pack, the charger, or the connection between them. On current Milwaukee manuals, hot/cold battery status is typically shown by a flashing red light only, not red-and-green. (documents.milwaukeetool.com)
Most likely causes:
Milwaukee chargers use electronic communication with the battery pack to monitor charge state, temperature, and charging safety. If that process fails, the charger stops charging and signals a fault with the flashing red/green indicator. Milwaukee’s manuals for several charger families consistently describe this LED state as “Fault.” (milwaukeetool.com)
This is important because many unofficial explanations on the internet mix up the meanings of the LEDs. In Milwaukee’s own documentation, the pattern is generally:
So if your charger is specifically alternating or blinking red and green, the most accurate interpretation is not “wait for temperature to normalize” alone, but rather “the charger sees a problem and is refusing to charge.” Temperature can still be part of the underlying problem in some cases, but the official hot/cold indication is a red flashing light, not the red/green fault code. (documents.milwaukeetool.com)
From an engineering perspective, the fault can be triggered by any interruption in the charger-to-pack verification path, including:
Milwaukee’s own troubleshooting step is very consistent across manuals:
Current Milwaukee documentation available in 2025–2026 for multiple charger models shows the same general behavior: red/green flashing = fault, while fast or plain flashing red = temperature out of charging range. Some newer/high-end chargers also add other states such as slow flashing red for charge pending or communication-related staging, but the red/green fault indication remains consistent. (documents.milwaukeetool.com)
A practical trend in modern cordless-tool systems is that chargers now rely heavily on battery intelligence and protection logic rather than simply applying current. That improves battery life and safety, but it also means that even a minor communication or contact problem can stop charging entirely. Milwaukee explicitly notes that its chargers communicate with the pack to monitor voltage, temperature, and charge status. (milwaukeetool.com)
If you want the shortest practical interpretation:
| LED behavior | Meaning | |
|---|---|---|
| Solid red | Charging | |
| Solid green | Fully charged | |
| Flashing red | Too hot / too cold | |
| Flashing red and green | Fault detected | (documents.milwaukeetool.com) |
If the battery itself shows an alternating pattern on its fuel gauge lights, that is a separate indication on some Milwaukee packs that the battery temperature is too high or another battery-side protection state exists. That is different from the charger LED fault signal, although the two can occur together if the pack is unhealthy. (documents.milwaukeetool.com)
Because this involves lithium-ion batteries, do not try unsafe “jump start” methods, bypass protection electronics, or open the pack unless you are properly trained and equipped. Milwaukee manuals explicitly say to never disassemble the battery or charger and to use a Milwaukee service facility for repairs. (documents.milwaukeetool.com)
Also avoid charging a battery that is physically damaged, wet, overheated, or shows signs of swelling or burning smell. Milwaukee warns against fluid exposure and short-circuit risk for chargers and packs. (documents.milwaukeetool.com)
Try these in order:
Remove and firmly reinsert the battery
Make sure it is fully seated in the bay. Milwaukee specifically calls this out as the first check for a red/green fault. (documents.milwaukeetool.com)
Power-cycle the charger
Unplug it for at least 2 minutes, then reconnect and try again. (documents.milwaukeetool.com)
Let the battery reach room temperature
If the battery was just used hard, or was left in a cold vehicle, let it sit indoors for a while. Even though red/green is a fault code, temperature stress can contribute to charging problems, and the official hot/cold state is flashing red. (documents.milwaukeetool.com)
Inspect and clean the contacts
With the charger unplugged, remove dust/debris from vents and electrical contact areas by brushing or vacuuming gently. (documents.milwaukeetool.com)
Cross-test if possible
If the red/green blinking persists, service or replace
Milwaukee’s manuals say persistent fault indication should be referred to a Milwaukee service facility. (documents.milwaukeetool.com)
If you want to diagnose it more precisely, useful next checks are:
With that information, the fault can usually be narrowed to contact issue, battery failure, or charger failure.
Short version: your Milwaukee charger blinking red and green means it has detected a fault, not normal charging. The first things to try are:
If it keeps doing it, the battery pack or charger likely needs service or replacement. If you want, I can help you identify which one is bad with a 3-step test.