How to Flash an Old Rechargeable Battery

If a rechargeable battery remains lying around off of its charger, it will not hold a charge. Eventually, as dendrite crystals build up within the battery, it will become unable to be recharged to full power. Dead nicad rechargeable batteries can be "flashed" back to life and full power. The process is as simple as jump-starting a car, but on a much smaller scale.

Flash Your Battery Back to Life.

Look at the battery and if it's corroded at all, stop here because it can't be flashed.

Ground the battery by hooking the black alligator clamp from the 12-volt battery charger to the negative end of the old nicad rechargeable battery. The negative end of a single cell battery is the flat end.

Use the red alligator clamp to "flash" the old rechargeable battery. Tap the positive, or raised, end of the single-cell nicad rechargeable battery with the red alligator clip. Sparks may spray out of the ends of the battery during this process.

Securely hold both the black and red alligator clamps to the battery for up to three seconds to complete the flashing process.

Remove the alligator clamps. Retest the battery with a battery tester to see if it has been charged.

Things You Will Need

  • 12-volt battery charger
  • Dead nicad batteries
  • Safety goggles
  • Insulated gloves
  • Long sleeve shirt
  • Battery tester


  • Take the necessary precautions to wear safety gear to protect your skin, eyes and handles during the flashing process.


  • Mishandling the nicad rechargeable battery can cause battery acid leaks, a fire or even an explosion.

About the Author

Deb Katula has written and researched for Societe Generale, FIMAT, Nikko Securities, Chicago Mercantile Exchange and Arthur Anderson. She holds an MBA in economics and finance from the University of Chicago; a Japanese language fellowship from Harvard; and a Bachelor of Arts in business/psychology/Asian studies from Augustana College.

Photo Credits

  • batteries isolated on white background image by Nikolay Okhitin from Fotolia.com