You're in the middle of a project. The drill dies. You swap the pack, slide it onto the DeWalt 20v lithium battery charger, and walk away to grab a coffee. When you come back, that little red light is doing something weird. Maybe it's a slow blink. Maybe it’s a frantic, "I’m about to explode" rapid pulse. Or maybe, and this is the worst, it’s doing nothing at all.
It's frustrating.
Most people think these chargers are just plastic bricks with some copper inside. They aren't. They’re actually pretty sophisticated computers that talk to the Battery Management System (BMS) inside your power tool packs. If that conversation goes south, your battery doesn't charge. Usually, it’s not even a broken charger; it’s just the charger being "smart" for its own good.
The Secret Language of the DeWalt 20v Lithium Battery Charger
Most folks ignore the little sticker on the front of the unit. You shouldn't. DeWalt uses a specific blink code to tell you exactly why your job is currently stalled. If the light is blinking steadily, it’s charging. Solid light? You’re good to go. But then there’s the "Hot/Cold Pack Delay."
If you’ve been pushing your circular saw through wet pressure-treated lumber, that battery is screaming. It’s hot. The DeWalt 20v lithium battery charger sees that internal temperature and refuses to push current. Why? Because charging a hot lithium-ion cell is a great way to start a fire or, at the very least, kill the lifespan of the pack. It’ll blink with a specific rhythm—long on, short off—until the cells cool down. Honestly, just leave it alone. Once it hits the right temp, it starts automatically.
Then there’s the "Broken" blink. That fast, erratic flashing usually means the charger has detected a dead cell or a high internal resistance. This is often where people give up and buy a new $150 kit. Don't do that yet.
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The "Jumpstart" Trick (Use with Caution)
Sometimes a battery sits too long. Lithium cells naturally drain over time, and if the voltage drops below a certain threshold—usually around 1.5V to 2V per cell—the DeWalt 20v lithium battery charger won't even recognize it’s plugged in. It thinks the cradle is empty.
I've seen guys in workshops "jump" these. They take a fully charged battery and use two jumper wires to connect the positive and negative terminals to the dead battery for about 30 seconds. This pushes just enough voltage into the dead pack so the charger can finally "see" it. It works. Usually. But keep in mind, you’re bypassing safety protocols. If the cell was dead because it was actually damaged, you're playing with fire. Literally.
Comparing the DCB107, DCB115, and the Yellow Fast Chargers
Not all chargers are created equal. If you got your tools in a Black Friday bundle, you probably have the DCB107. It’s the small, black, slow one. It puts out about 1.25 amps. If you’re trying to charge a 6.0Ah FlexVolt battery on that thing, you might as well go take a nap. It’s going to take four or five hours.
The DCB115 is the mid-range workhorse. You see it everywhere. It pumps out 4 amps. That’s a massive jump. It’ll top off a standard 2.0Ah compact battery in about 30 minutes.
Then you have the yellow "Fast Chargers" like the DCB118 or the DCB1112. These are beasts. Some of them have internal fans because they’re pushing 8 to 12 amps. You can hear them whirring from across the garage. They’re designed for the heavy-duty user, but here’s the trade-off: heat. Fast charging creates heat. Heat kills lithium batteries. If you aren't in a rush, using the "slow" DeWalt 20v lithium battery charger actually makes your expensive batteries last more years. It's a turtle and the hare situation.
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Why Your Charger Might Actually Be Fine
Before you toss your charger in the bin, check the terminals. These things live on construction sites and in dusty garages. Sawdust is an insulator. If a tiny layer of fine pine dust gets into the female receptors of the battery or the male leads on the charger, the connection fails.
Take a Q-tip. Dip it in a bit of rubbing alcohol. Clean those contacts. You’d be surprised how many "broken" chargers are just dirty.
Also, check your power source. These chargers are sensitive to "dirty" power. If you’re running it off a cheap, non-pure sine wave inverter in your truck, or a long, thin extension cord that’s seeing a massive voltage drop, the charger might error out. It wants a clean 120V signal.
Counterfeit Chargers: A Dangerous Game
You’ll see them on Amazon and eBay for $20. They look almost identical to the OEM DeWalt units. They might even have a fake logo. Stay away.
Inside a real DeWalt 20v lithium battery charger, there are thermal sensors and complex circuitry to prevent overcharging. The knock-offs often lack these. They just shove raw current into the battery. At best, they fry your $100 battery pack. At worst, they cause a thermal runaway event in your garage. Stick to the genuine yellow and black stuff. It’s expensive because it won't burn your house down.
What About FlexVolt?
The 20v/60v FlexVolt batteries are a feat of engineering. They change their internal wiring based on what tool they’re plugged into. But when it comes to charging, they still use the same DeWalt 20v lithium battery charger interface.
The charger doesn't care that it's a 60v battery; it charges it in its 20v parallel configuration. This is why a FlexVolt battery takes so long to charge on the basic units. You’re essentially charging three batteries at once through one port. If you own FlexVolt glass, you basically have to upgrade to the DCB118 or a multi-port station.
Maintaining Your Charging Station
Don't leave your batteries on the charger for months. Yes, the charger has a "maintenance mode," but it’s still better to pull them off once that solid red light hits.
Avoid charging in freezing temperatures. If your garage is 30 degrees Fahrenheit, bring the charger inside. Chemical reactions in lithium batteries don't like the cold. Charging at sub-freezing temps can cause permanent "lithium plating" on the anode, which ruins the battery's capacity forever. Basically, if you’re uncomfortable without a jacket, your battery is uncomfortable too.
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Real-World Troubleshooting Steps
If you're staring at a light that won't turn on, try this specific sequence:
- Unplug the charger from the wall for 60 seconds. This resets the internal logic.
- Check the battery for any physical cracks. If the casing is cracked, moisture might have tripped the internal fuse.
- Slide the battery on firmly. Sometimes you have to give it a "thunk" to seat it properly.
- Check the outlet with a lamp or another tool. I've spent twenty minutes troubleshooting a charger only to realize the GFCI outlet had tripped.
Actionable Next Steps
If your charger is dead and out of warranty, don't try to open it unless you know what a capacitor is—those things can hold a charge even when unplugged. Instead, look for "Type 1" vs "Type 2" stickers on the bottom to ensure you buy a compatible replacement.
Keep your charging area ventilated. If you're mounting it to a wall, leave an inch of space behind it for airflow. Most importantly, if you have a battery that "fails" on the charger, try it on a second charger (maybe a friend's) before you recycle the pack. Often, the pack is fine, and it’s just a communication error with one specific charging unit.
Clean your contacts today. Grab some isopropyl alcohol and spend two minutes wiping down the metal tabs on your batteries and the charger. It prevents 90% of the "no-charge" errors people face. If you're still seeing a fast-blinking red light after cleaning, it's time to look into the DeWalt warranty—they are surprisingly good about replacements if you're within the three-year window.