How to Restore 18V Batteries

Written by hank macleod
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How to Restore 18V Batteries
A "bad" battery pack can work just like new after proper care. (drill image by Albert Lozano from

Throwing out and replacing non-functioning battery packs is hazardous to the environment and expensive. Exercise and recondition rechargeable workshop battery packs every few months to keep them fresh. Otherwise, crystals form within the battery, reducing the charge capacity and degrading performance. Refurbish your old battery packs to break up the crystalline formation and bring them back to life. One quick method involves using a higher voltage and current to shock your battery pack multiple times, restoring the potential difference to 18 volts. Borrow a MIG welder if you do not have one, as the high voltage and amperage is sufficient for 18 volt battery pack refurbishment.

Skill level:

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Things you need

  • 5 or 6 inches of 12-gauge wire
  • Electrical tape
  • MIG welder
  • Welder goggles/shield
  • Welding gloves

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  1. 1

    Insert the affected battery pack into an appropriate portable power tool such as a cordless drill. Run the appliance until there is no sign of battery life. Remove the battery pack.

  2. 2

    Insert the test leads of a voltage meter into the battery terminal holes located at the top of the battery so that each lead is touching the respective metal lining. Swap the leads if the meter reads negative. Mark the negative battery terminal indicated by the black lead for later use. Take note of the tested voltage, which is likely well below 18V. Remove the test leads.

  3. 3

    Insert a 2- to 3-inch length of 12-gauge copper wire into each battery terminal hole. Push down as far as they will go. Bend each wire to a 90-degree angle, facing away from each other. Wrap electrical tape over the gap between the wires, securing them while leaving at least an inch of bare wire at the tips.

  4. 4

    Identify the positive and negative leads of the MIG welder. Clamp the alligator ground clip to the respectively charged wire in the battery pack terminal--e.g., if the clip is negative, attach it to the negative terminal wire. Keep the opposite wire clear. Drive a 3-inch length of wire electrode from the gun.

  5. 5

    Put on all proper safety equipment. Hold the welder gun clear of any other object. Turn on the welder, but leave the gas off. Touch the gun electrode to the terminal wire OPPOSITE to the grounded (clamped) wire. Repeat 15 times, taking care not to touch anything else with the gun. Turn off the welder and unclamp the ground clip.

  6. 6

    Touch the voltage meter test leads to the respective battery terminal wires. Check that the voltage is closer to 18V. Repeat Step 5 until the meter reads at least 17.5V. Pull out the wires from the battery terminals. Insert the battery pack into its charger and allow it to charge overnight.

Tips and warnings

  • Ask for assistance if you are unfamiliar with a MIG welder.
  • You can make money restoring battery packs.
  • Even though the gas is off, the welder gun produces sparks. Keep away from flammable materials and liquids.
  • Always use proper safety equipment.
  • Wait for the battery pack to cool before use.

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