Power Tool Battery Won’t Charge? Common Causes & Fixes

Key Points

• A battery that won't charge is usually caused by a dirty connection, a temperature issue, a charger fault, or a battery that has reached the end of its life.
• Flashing lights on your charger are not random. Most brands use them to tell you exactly what is wrong.
• Never try to jump-start a lithium-ion power tool battery with jumper cables or a car battery. It is a real fire risk, no matter what a video online tells you.
• Testing the battery in a different charger is the fastest way to figure out if the problem is the battery or the charger.
• If simple troubleshooting does not work, Witmer Motor Service can test, repair, or replace your power tool battery safely.

A power tool battery that won't charge can bring a job to a stop. The good news is most causes are simple, and many are fixable without buying a new battery.

At Witmer Motor Service, we have been an authorized power tool sales and service center for years, working on Milwaukee, DeWalt, Makita, Metabo, Fein, and more. Here is how our technicians approach the problem.

Start With the Charger's Warning Lights

Most modern chargers use flashing lights to tell you what is wrong before you touch the battery.

• Solid or flashing red: Charging normally, or too hot or cold to charge.
• Flashing red and green together: The battery is likely defective.
• No light at all: The charger may not be receiving power.

Check your charger's manual to confirm what your lights mean, since this varies by brand. If you cannot find yours, our power tool parts department can help you identify the correct charger and battery for your tool.

7 Common Causes of a Battery Not Charging

1. Dirty or Corroded Contacts

Dust and light corrosion on the battery or charger contacts can block the connection.

Fix: Unplug the charger and gently wipe both sets of contacts with a dry cloth or pencil eraser.

2. The Battery Is Too Hot or Too Cold

Lithium-ion batteries have built-in thermal protection. Above roughly 140°F, or very cold, the charger will refuse to start.

Fix: Let the battery return to room temperature, then try again.

3. Loose Connection on the Charger

Some chargers need the battery to click firmly into place.

Fix: Remove the battery and slide it back on with firm, even pressure.

4. A Faulty Charger, Not the Battery

Sometimes the charger is the actual problem.

Fix: Test the battery on a different, compatible charger. If it charges there, your charger needs service. We repair chargers for most major brands through our power tool sales and repair team.

5. A Deeply Discharged Battery

If a battery sits dead too long, it can drop below the voltage needed to signal the charger to start. This looks like a defective battery but is not always the same problem.

6. Imbalanced or Failing Cells

Power tool batteries are made of several cells wired together. Over time, some wear out faster than others, and the internal management system may stop charging altogether to protect the pack.

7. The Battery Has Reached the End of Its Life

Rechargeable batteries have a limited number of charge cycles. After enough cycles, capacity drops and the battery may stop accepting a charge.

According to the Consumer Technology Association, lithium-ion batteries typically last 300 to 500 full charge cycles before performance declines significantly. When it is time for a fresh one, we carry replacement batteries and power tool accessories for most major brands.

What Not to Do

You may see videos claiming you can revive a dead battery with jumper cables and a car battery.

We strongly advise against this.

• It bypasses the battery's built-in safety electronics.
• It can cause overheating, swelling, or fire.
• Even when it appears to work, it does not fix the underlying problem.

The U.S. Consumer Product Safety Commission publishes guidance on lithium-ion battery safety, and DIY jump-starting is not a method any manufacturer recommends. If a battery will not charge, proper testing is the safer path, not an internet workaround. Our team can test your battery safely instead.

Simple Troubleshooting Steps to Try First

1. Check the outlet with another device to confirm it has power.
2. Inspect and clean the contacts on the battery and charger.
3. Confirm the battery is at room temperature.
4. Reseat the battery firmly on the charger.
5. Try a different, compatible charger if available.
6. If none of this works, bring it to our shop for professional testing.

When to Repair vs. Replace

Not every battery that won't charge needs to be thrown out.

• Repair or testing makes sense if the battery is fairly new, was working recently, or the charger tests fine with another battery.
• Replacement makes sense if the battery is several years old, has been dropped, or shows swelling.

Our team at Witmer Motor Service can test your battery and charger and give you an honest answer. Since we sell power tools and service them, we have no reason to push a replacement you do not need.

Frequently Asked Questions

Why does my power tool battery show a flashing red light and not charge?

This usually means the battery is too hot or cold to safely charge, or on some brands, that it failed testing. Let it reach room temperature and try again. If the light continues, bring it in for service.

Can a completely dead power tool battery be recharged?

Sometimes. If it is deeply discharged but not damaged, a professional test and controlled recharge can often bring it back. If internal cells have failed, it cannot be safely restored.

Is it safe to try the jumper cable trick to fix my battery?

No. Applying unregulated current to a lithium-ion battery bypasses its safety protections and creates a real risk of fire. No manufacturer recommends this method.

How long should a power tool battery last before it needs replacing?

Most lithium-ion power tool batteries last 300 to 500 full charge cycles, or roughly 2 to 4 years of regular use, before capacity drops noticeably. We stock replacement batteries in our power tool parts collection.

Should I replace the battery or the charger first?

Test the battery on a different, compatible charger if possible. If it charges normally there, your original charger is the problem. If it still won't charge, the battery is likely the issue. Either way, our power tool repair team can confirm which one needs attention.

How Witmer Motor Service Can Help

We have been a trusted power tool and electric motor sales and service company since 1964, and we are an authorized service center for major tool brands.

Our team can:

• Diagnose whether the issue is the battery, the charger, or the outlet
• Repair and service the power tools you already own, including Milwaukee, DeWalt, and Makita tools
• Recommend a replacement battery or charger when it is truly needed
• Help you choose the right tool if you are shopping for something new

Visit our Power Tool Sales and Repair page to learn more, or stop by our New Holland, PA location. Not local? Ask about our pickup and delivery service. You can also read what our customers say on our testimonials page.