Rebuild a Cordless Tool Battery

An affordable alternative to a new battery pack

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Cordless tool batteries eventually fail, but replacement batteries can be amazingly expensive. To save money, consider rebuilding the battery pack.

Tools Required

  • 4-in-1 screwdriver
  • Hot melt glue gun
  • Soldering iron
  • Spring clamps

Materials Required

  • Replacement battery cells
  • Rosin-core solder
  • Tape
  • Wire

Power Tool Batteries: Replace the Cells in the Battery Pack

When your power tool battery pack bites the dust, probably your first inclination is to buy a new one. But if the battery is out of production or the price of a new one is sky high, consider rebuilding it yourself instead of paying a professional rebuilder. That’ll save you about $25. You’ll need new cells, a soldering iron and rosin-core solder, a glue gun, and some wire and tape. The whole process takes about an hour.

Most power tool battery packs use 1.7-in. x .9-in. “Sub C” size batteries. Remove the screws that hold the pack together and yank the top off. Then remove the cluster of batteries and measure one of the cells. Then get the milliamp-hour (mAh) rating off the old batteries (or search online for the cell specs). If you’re willing to spend more, upgrade to cells with a higher mAh rating—they hold more juice. Just make sure they have a discharge rating of 5C or higher. And always buy cells with the tabs already welded in place ( is one online battery seller). Then get to work.

Project step-by-step (2)

Step 1

Arrange and Glue

rebuild cordless tool battery hot glue

Lay out the first row of new cells on a flat surface and arrange the polarity and solder tabs in the same direction as the old pack, using the old battery pack as a template. Then glue them together with a hot-melt glue gun. This isn't the only thing you can do with hot glue. Check out 19 of our favorite hot glue hacks.

Step 2

solder the cells battery pack

Protect the battery by clamping a heat sink onto the tabs before you apply heat. Then solder the tabs together with rosin-core solder. Duplicate the process with the additional rows of cells. Transfer the temperature sensor and insulators from the old battery and reinstall in the plastic case. Charge it up, test it out and start your next home improvement project.

These 11 power tools all pack quite a punch, and all without plugging into the wall. Check out these editor-approved gift ideas for DIYers with nary a cord in sight.