Appliance Repair

How to Revive NiCad Rechargeable Battery

By Editorial Team Published · Updated

How to Revive NiCad Rechargeable Battery

How to Revive NiCad Rechargeable Battery click here to view:

How to revive NiCad Rechargeable Battery Our cordless phone was disconnected with its base during our14-day Europe trip, thus the rechargeable on the phone set is dead. After recharging it in the base overnight, nothing indicated it had any charge. It is dead because of the crystal denrite growth. How can you revive it? Simple, it only takes 2 minutes and a charger to “zap” it.

For the full video tutorial, visit Genius Asian.

Understanding Why NiCad Batteries Die

NiCad (Nickel-Cadmium) batteries suffer from a well-known problem called crystalline dendrite growth, sometimes referred to as “voltage depression” or the “memory effect.” When a NiCad battery sits unused for an extended period — or is repeatedly charged without being fully discharged first — tiny crystalline structures form inside the cells. These dendrites create internal short circuits between the positive and negative plates, preventing the battery from holding a charge.

The good news is that these crystals can often be broken down with a brief, high-current pulse that essentially vaporizes the thin crystalline bridges. That is what the “zap” method in the video demonstrates. But there are several other proven approaches worth knowing about.

Alternative Methods for Reviving NiCad Batteries

1. Conditioning Charger (Discharge-Then-Charge Cycle)

When to use: Batteries that hold some charge but have noticeably reduced run time.

  • A conditioning charger like the La Crosse BC-700 or Opus BT-C3100 automatically discharges the battery to near-zero, then recharges it fully. This controlled cycling breaks down mild crystalline buildup over multiple cycles.
  • Pros: Gentle on the battery, automated, extends battery life long-term, works on individual cells
  • Cons: Takes several hours per cycle, may need 3-5 cycles for badly degraded batteries, charger costs $30-50
  • Difficulty: Easy
  • Estimated cost: ~$30-50 for the charger (reusable for all future batteries)

2. Freezer Method

When to use: Batteries that will not charge at all and have nothing to lose.

  • Wrap the battery pack in a sealed plastic bag (push out all air to prevent condensation). Place it in the freezer for 12 to 24 hours. Remove it, let it warm to room temperature for at least 2 hours, then attempt charging.
  • The theory is that extreme cold contracts the crystalline structures enough to break some of the dendrite bridges. Results are inconsistent, but this method has worked for many people on cordless phone and power tool battery packs.
  • Pros: Free, no special equipment, worth trying on otherwise-dead batteries
  • Cons: Inconsistent results, may only provide temporary improvement, condensation risk if the bag is not sealed properly
  • Difficulty: Easy
  • Estimated cost: ~$0

3. Capacitor Discharge Method (High-Current Pulse)

When to use: Completely dead batteries that will not respond to a charger.

  • This is the more controlled version of the “zap” shown in the video. You charge a large electrolytic capacitor (1,000 to 4,700 microfarads, rated at the battery’s voltage or higher) from another power source, then briefly touch the capacitor’s leads to the dead battery’s terminals. The instantaneous high-current discharge is often enough to vaporize the dendrite bridges.
  • Safety warning: This method involves a brief but very high current. Wear safety glasses. Make the connection quickly — holding it for more than a fraction of a second can overheat the cell. Never attempt this on swollen, leaking, or physically damaged batteries.
  • Pros: Very effective on fully dead cells, fast, requires minimal equipment
  • Cons: Requires basic electronics knowledge, risk of overheating if done wrong, not effective on mechanically failed cells
  • Difficulty: Medium
  • Estimated cost: ~$3-5 for a capacitor from an electronics store

4. Spot Welder / Battery Tab Replacement

When to use: One or two cells in a multi-cell pack have failed while the rest are fine.

  • Open the battery pack, test each cell individually with a multimeter, and replace the dead cells with new ones of the same capacity and chemistry. Use a spot welder (or carefully solder with flux) to attach nickel tabs.
  • Pros: Saves the cost of a whole new pack, ideal for expensive cordless tool batteries
  • Cons: Requires a spot welder or good soldering skills, matching cell capacity is important, voids warranty
  • Difficulty: Hard
  • Estimated cost: ~$2-5 per replacement cell

Tips and Tools

  • Multimeter is essential. Before attempting any revival method, use a multimeter to measure the battery’s voltage. A fully dead NiCad cell reads close to 0 volts. A healthy 1.2V cell that reads 0.8V or higher may just need conditioning.
  • Label your batteries. Write the date of purchase on each rechargeable battery with a permanent marker. NiCad batteries typically last 500-1,000 charge cycles, so knowing their age helps you decide if revival is worth the effort.
  • Do not mix old and new cells. If you are rebuilding a multi-cell pack, replace all cells at once. Mixing cells of different ages causes the weakest cell to drag down the whole pack.
  • Consider upgrading to NiMH. If your NiCad battery is for a cordless phone, check if a NiMH (Nickel-Metal Hydride) replacement is available. NiMH batteries have higher capacity, less memory effect, and do not contain toxic cadmium. Panasonic Eneloop and EBL are reliable budget picks.
  • Proper disposal matters. Dead NiCad batteries contain cadmium, a toxic heavy metal. Never throw them in the trash. Take them to a battery recycling drop-off at Home Depot, Lowe’s, or your local hazardous waste facility.

If you are working on other cordless appliance repairs, you might also find our guide on rice cooker repair helpful — small appliance troubleshooting follows many of the same diagnostic steps.

When to Call a Pro

Most battery revival work is safe DIY territory, but there are situations where you should step back:

  • Swollen, leaking, or hot batteries. A battery that is bulging, oozing liquid, or warm to the touch when not in use may have an internal short that cannot be fixed. Do not attempt to charge or zap it. Take it to a battery recycling center immediately.
  • Lithium-ion battery packs labeled as NiCad. Some older devices had NiCad batteries that were later replaced with lithium-ion packs in the same form factor. Applying NiCad revival techniques to a lithium-ion battery is dangerous and can cause a fire. Always check the label on the cells inside the pack.
  • High-voltage battery packs (above 24V). Cordless tool packs with many cells in series carry enough voltage to deliver a painful shock. If you are not comfortable working with electronics, take the pack to a battery rebuild service. Many local shops rebuild DeWalt, Makita, and Milwaukee packs for $40-60.

For more on staying safe with home electrical projects, see our electrical safety guide.

Always verify contractor licensing and insurance in your state. Cost estimates are averages and may vary by location.