DeWalt batteries rarely need jump-starting, but you can revive a deeply discharged pack

A DeWalt battery that won't charge is usually too deeply discharged to wake up on its own. The charger sees zero voltage and stops trying. You can force current through the battery to bring it back to life, but the method depends on whether the battery is a lithium-ion pack (20V, 60V, FlexVolt) or an older nickel-cadmium type. Most modern DeWalt users have lithium-ion, and those respond to a controlled trickle charge from a working charger or a parallel connection to a live battery.

The fastest and safest route is to use a second working DeWalt battery of the same voltage and a charger designed for that voltage. You can also use a bench power supply if you have one and know the battery's voltage and polarity. Do not attempt to jump-start a swollen, cracked, or leaking battery—discard it instead.

Key Takeaways

  • A completely dead DeWalt lithium-ion battery will not charge until you push current through it to raise its voltage above the charger's minimum threshold, usually around 2 to 3 volts.
  • The safest method is to connect the dead battery in parallel with a working battery of the same voltage using jumper cables or a parallel charging adapter, then place both in a charger.
  • You can also hold the dead battery's terminals against a working battery's terminals for 10 to 30 seconds to deliver a small charge, then when ready place it in the charger.
  • Never attempt this on a swollen, cracked, or leaking battery, and never exceed the charger's rated voltage or current.
  • If the battery still will not charge after one attempt, the internal protection circuit or cells are likely damaged and the battery should be replaced.

Why a DeWalt battery stops accepting a charge

DeWalt lithium-ion batteries have a built-in protection circuit that cuts power when voltage drops below a safe level—usually around 2 volts per cell. This is meant to prevent damage, but it also means the charger cannot detect the battery and will not send current to it. The battery is not dead; it is asleep.

Older nickel-cadmium and nickel-metal hydride DeWalt batteries can develop a memory effect if charged before they are fully discharged, but they rarely drop so low that a charger refuses them. Lithium-ion packs are more prone to this problem because they are more sensitive to over-discharge.

The parallel connection method (safest for lithium-ion)

Connect the dead battery to a working battery of the same voltage using two jumper cables or a parallel charging adapter. Red to positive, black to negative. Hold the connection for 30 seconds to a minute. This pushes a small amount of current through the dead battery and raises its voltage enough for the charger to recognize it.

After 30 seconds, disconnect the batteries and place the previously dead battery in the charger alone. It should begin charging. If the charger shows an error light or does not start within a few seconds, try the parallel connection again for another 30 seconds, then recharge.

Do not leave the batteries connected in parallel for more than a minute or two. The working battery will continue to discharge into the dead one, and you risk overheating both.

The terminal-touch method (quick but less controlled)

If you do not have jumper cables or a parallel adapter, you can touch the positive and negative terminals of the dead battery directly to the corresponding terminals of a working battery. Hold the contact for 10 to 30 seconds. This delivers a brief current spike that can wake up the protection circuit.

Use a working battery of the same voltage. Do not hold the contact longer than 30 seconds, and do not let the terminals arc or spark. After the brief contact, place the dead battery in the charger when ready.

This method is faster but less precise than a parallel connection. It works well for lithium-ion packs but can be risky on older battery types, so use it only if you are confident the batteries are both lithium-ion.

Using a bench power supply to revive a dead battery

If you have a variable bench power supply, you can set it to the battery's rated voltage (20V, 40V, 60V, or 120V for FlexVolt) and connect the positive and negative leads to the battery's terminals. Start at zero volts and slowly increase to the rated voltage over 10 to 15 seconds, then hold it for 30 to 60 seconds.

This method gives you the most control and is the gentlest on the battery. However, it requires equipment most homeowners do not have. If you do use a bench supply, set the current limit to 1 amp or less to avoid overheating the battery's internal cells.

After the voltage has been applied, disconnect the power supply and place the battery in its charger. The charger should now recognize the battery and begin a normal charge cycle.

What to do if the battery still will not charge

If the battery does not charge after one or two attempts at jump-starting, the internal protection circuit or the cells themselves are likely damaged. Lithium-ion batteries have a limited lifespan, and deep discharge can shorten it further. At this point, the battery is not worth reviving.

Check the warranty on your DeWalt battery. Most DeWalt batteries carry a three-year limited warranty, and some failures are covered even if the battery was over-discharged. Contact DeWalt customer service with your battery's model number and serial number (usually printed on the label) to ask about a replacement.

If the warranty has expired, a replacement battery of the same voltage usually costs between $50 and $150, depending on the amp-hour rating. A higher amp-hour battery (5.0 Ah or 6.0 Ah) costs more but holds a charge longer and runs tools for longer periods.

Signs a battery should not be jump-started

Do not attempt to revive a battery that is swollen, cracked, leaking, or visibly damaged. A swollen battery indicates internal pressure from a failed cell, and explore current can cause it to rupture or catch fire. Discard it safely by taking it to a battery recycling center or a retailer that accepts old batteries (most big-box hardware stores do).

If the battery smells like chemicals, feels hot to the touch, or has white or blue residue on the terminals, do not use it. These are signs of internal failure. Set it aside in a safe place and replace it.

Frequently Asked Questions

Can I jump-start a DeWalt battery with a car battery?

No. A car battery is 12 volts, and most DeWalt power tool batteries are 20 volts or higher. The voltage mismatch will damage the battery's protection circuit or cells. Use only a DeWalt battery of the same voltage.

How long does it take to jump-start a dead DeWalt battery?

The jump-start itself takes 30 seconds to a minute. After that, the battery will charge normally in the charger, which usually takes 30 minutes to two hours depending on the battery's capacity and the charger model.

Will jump-starting a battery damage it?

A controlled parallel connection or brief terminal contact will not damage a healthy battery. However, if the battery was over-discharged because of a manufacturing defect or internal failure, the damage is already done. Jump-starting will not make it worse, but it may not fix it either.

Can I jump-start a DeWalt FlexVolt battery the same way?

Yes. FlexVolt batteries are lithium-ion and respond to the same parallel connection or terminal-touch method as standard DeWalt batteries. Use a working FlexVolt battery or a standard DeWalt battery of the same base voltage (60V FlexVolt with 60V standard, for example).

What if my charger shows an error code after I jump-start the battery?

Some DeWalt chargers display an error if the battery voltage is still too low or if the charger detects a problem with the battery's cells. Try the jump-start again for another 30 to 60 seconds, then recharge. If the error persists, the battery's internal circuit or cells are likely damaged and the battery should be replaced.