How to fix drill batteries

Written by kathryn rateliff barr Google
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How to fix drill batteries
NiCd batteries can fail to hold a charge if they are frequently overcharged. (Hand yelow drill isolated image by Marek Kosmal from

Cordless drills use rechargeable batteries as a power source. According to the website RechargeableBattery, Craftsman, Black and Decker, Bosch, Dewalt, Ryobi, Makita, Panasonic, Ridgid, and Milwaukee all use rechargeable nickel-cadmium, or NiCd, batteries as the main power source for their cordless drills.

NiCads fail either because they overheat during use or charging, they suffer polarity reversal, or they develop a weak battery charge memory. There are ways you can help your NiCd batteries hold a charge again.

Skill level:

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Things you need

  • 18v Nickel-cadmium power tool battery that will not hold a charge
  • 6v batteries
  • Digital multimeter
  • Copper hookup wire (16 or 18 AWG)
  • Wire stripper (optional)
  • Clock with second hand
  • Freezer
  • Freezer bags

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  1. 1

    Place the battery in a double-lock freezer bag and put it in the freezer for eight to 10 hours.

  2. 2

    Remove the battery from the freezer, but leave it in the freezer bag.

  3. 3

    Allow the battery to warm to room temperature. This thawing process may take longer for larger batteries, such as laptop computer batteries. Be sure the battery is completely thawed before continuing.

  4. 4

    Fully charge the battery, using the approved charger and manufacturer's instructions for charging. This process can be repeated up to five times during the life of the battery.

  1. 1

    Use a digital multimeter, or DMM, to measure the battery voltage. Turn on the DMM, and set it to measure the rated voltage of the battery. Place the red lead on the positive battery pole and the black lead on the negative pole. Read the meter and record the value. If the display shows a number that is at least half of the battery's rated voltage, the positive lead is on the negative battery pole. If the display reads a negative value of one or two volts, your DMM leads are correctly oriented, but the battery polarity has reversed. Keep track of which pole is which.

  2. 2

    Refer to charts at to determine the voltage and time parameters necessary for battery recovery. For the purpose of this example, we will connect four 6v lantern batteries in a series to recharge an 18v drill battery.

    Take your copper hookup wire and strip a small section at each end. Wrap one stripped section around the positive pole of the first battery, and the other end around the negative pole of the second battery. Repeat this process to connect the positive pole of battery two to the negative pole of battery three. Repeat again to connect the positive pole of battery three to the negative pole of battery four.

    Do not complete the circuit with the last pair of terminals. The last two terminals are the positive and negative terminals of the 24v source.

    Wrap one stripped end of a longer wire to the positive terminal of battery one in your power source, and wrap a second long wire to the negative terminal of battery four. Strip the loose ends only far enough to make contact with the drill battery terminal. These wires should be long enough to reach comfortably between your power source and your power tool battery.

  3. 3

    Connect the battery series negative terminal wire to the negative terminal of your drill battery. Touch the positive terminal wire to the positive battery terminal three times per second for 10 seconds, or as quickly as you can. Let the battery cool for 15 minutes.

  4. 4

    Place the battery in its charger for 15 minutes, then remove it. Measure the voltage with the DMM. Wait 60 minutes and remeasure the voltage.

    If the two readings are about the same--i.e., within plus or minus 0.3 volts--the battery has been repaired and you may fully charge it. If the second reading is significantly lower, the battery was not repaired and you should repeat Step 3. You may repeat this process up to 25 times over the life of the battery.

Tips and warnings

  • Use goggles when surge-charging your battery.
  • Surge-charge your battery every six months to maintain its life.
  • Overcharging batteries shortens battery life. See manufacturers' recommendations for suggested charging times.
  • Do not surge the battery while it is hot; this may cause it to explode. Allow the battery to rest at least 15 minutes between surges.

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