If a covered Milwaukee M12 or M18 charger alternates red and green, its manual identifies a fault with the battery pack and/or charger. The light does not tell you which one has failed. Reseat the battery first; if the pattern continues, try the charger reset specified in the manual for your exact model. If it still flashes, stop and contact a Milwaukee service facility.
What alternating red and green means
The operator manual describes the pattern as “Flashing red/green: Damaged or faulty battery pack and/or charger.” The “and/or” matters: the indicator does not establish that the battery alone is bad. The reviewed guidance applies to the charger models covered by that manual, not necessarily every Milwaukee charger. Check the model number and its operator manual before applying these steps.
Other indicator patterns mean different things in the cited manual. Fast-flashing red signals a temperature condition affecting the battery and/or charger; charging begins when the temperature is within range. Slow-flashing red indicates charge pending in the described charger context. Neither pattern should be confused with alternating red and green.
How to troubleshoot the fault safely
- Reseat the battery. Remove the pack, then insert it again so it is properly seated. See the Milwaukee guidance on battery and charger troubleshooting.
- Reset the charger if the light continues. For the model covered by the cited manual, remove the battery pack or packs, unplug the charger for at least two minutes, plug it back in, and reinsert the pack. The operator manual’s indicator guidance specifies this sequence.
- Stop if the fault remains. Contact a Milwaukee service facility rather than attempting an internal repair. The manual recommends service for a persistent fault. See the operator manual and Milwaukee’s troubleshooting guidance.
- If you have compatible equipment, cross-test to narrow down the cause. Try the suspect battery on a known-good compatible charger, or a known-good compatible battery on the suspect charger. This is an isolation suggestion based on the manual naming either component as a possible fault source—not a manufacturer-prescribed repair or diagnostic procedure. Stop if the fault persists.
Do not open a lithium-ion battery pack, bridge its terminals, or try to “jump-start” it. Those actions are not supported by the reviewed official manuals; persistent faults should go to Milwaukee service.
#1 Best Overall
- Product will either come in original packaging that is in less than perfect shape and has been opened to inspect contents or will come in non-retail packaging (brown/white box or white/clear bag). Charges pack up to 40% faster, reducing downtime and maximizing productivity.
- The charger accepts all M18 and M12 batteries, providing an upgrade for both systems.
- The charger indicates when the battery reaches an 80% charge.
- Single unit simplicity for quick charge of all M12 and M18 battery packs.
- Sequential charging: automatically charges the second inserted pack once the first pack is fully charged.
Should you replace the battery or the charger?
Do not choose a replacement based on the alternating light alone. First establish whether the pack or charger is implicated, if possible, and confirm compatibility using the exact model numbers and manuals.
Milwaukee lists its M18 & M12 Rapid Battery Charger, model 48-59-1808, as charging all M12 and M18 batteries. It is a possible charger replacement only if the charger is the component implicated; verify that it fits your needs and equipment. A compatible M12 or M18 battery pack is a possible replacement only if evidence points to the pack. If the fault remains unclear, contact Milwaukee service rather than buying parts based on the light alone.
Rank #2
- DUAL CHARGING: This charger can tackle both 18 and 12 volt Milwaukee batteries, holding one of each in the unit at the same time.
- SEQUENTIAL CHARGING: Do not worry about managing charge cycles. This will take care of your batteries one at a time, devoting full charging power to each one.
- BATTERY COMMUNICATION: The charger has a chip that communicates with its batteries, keeping track of how much they have charged. It saves you power by reducing the amount of charge produced as the battery reaches full charge.
- FAST ACTING: Compact batteries can be fully charged in as little as 30 minutes, while extended life batteries can be charged in as little as a single hour.
- INDICATOR LIGHTS let you know whether a battery is charging, fully charged, and whether it needs maintenance or not.
If it flashes red and green with no battery installed
The reviewed guidance does not establish what this pattern means when no battery is installed. Identify the charger’s exact model and consult its operator manual or Milwaukee service. Do not assume the battery-related troubleshooting steps apply to this situation.
Quick Recap
Best Value
- This charger can tackle both 18 and 12 volt Milwaukee batteries, holding one of each in the unit at the same time.
- Compact batteries can be fully charged in as little as 30 minutes, while extended life batteries can be charged in as little as a single hour.
- The charger has a chip that communicates with its batteries, keeping track of how much they have charged. It saves you power by reducing the amount of charge produced as the battery reaches full charge.
- Indicator lights let you know whether a battery is charging, fully charged, and whether it needs maintenance or not
- In easy-to-open bulk packaging to pass the savings on to you.
Rank #4
- M18 six pack sequential charger
- The product is easy to use and easy to handle
- The product is highly durable
Rank #3
- Replacement for 12V battery charger 48-59-2401, 48-59-1812, 48-59-1201, 48-59-1807, 48-59-1204, 48-59-1810, 48-59-1808 and 18V battery charger 48-59-1804 48-59-1802 48-59-1806
- Compatible with all MIL 12V lithium-ion batteries 48-11-2401, 48-11-2440, 48-11-2460, 48-59-2420, 48-11-2430, 48-11-2411 and all 18V lithium-ion batteries 48-11-1862, 48-11-1880, 48-11-1850, 48-11-1852, 48-11-1812
- Supports 100-240V AC input, 10.8V-18V 3.0A DC Output. Can charge 12V and 18V batteries in less than an hour for jobsite efficiency.
- Indicator lights that show the status as batteries are charged and maintained. The built-in high-end protection board provides overcharge, overcurrent and high voltage protection for your mobile devices, ensuring the stability of the charging current.
- This Charger comply with FCC RoHS and CE security testing standards. Contact us: any question please click the "Ask a question" on our storefront or in "YOUR ORDER" options click the "contact seller".
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon at the time of purchase will apply.
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