Easiest Way to Revive a NiCad Rechargeable Battery

What This Video Shows

In this video I show you how to revive a dead NiCad (nickel-cadmium) rechargeable battery using a simple zap technique. Our cordless phone was disconnected from its base during our 14-day Europe trip, and when we returned, the rechargeable battery was completely dead. After recharging overnight in the base, there was still no sign of life whatsoever. The battery appeared to be permanently dead. But using a quick two-minute zapping technique with a separate charger, I was able to break through the crystal dendrite growth that was preventing the battery from holding a charge, and the battery came back to life.

Why This Matters

Before you throw away a seemingly dead NiCad rechargeable battery and buy a replacement, try this revival technique first. NiCad batteries are prone to a phenomenon called crystal dendrite growth, where crystalline structures form inside the battery over time, especially when the battery is left in a discharged state for extended periods. These dendrites create internal short circuits that prevent the battery from accepting a charge through normal means. However, a brief high-current pulse, or zap, can physically break apart these dendrites and restore the battery’s ability to charge and discharge normally.

How the Zap Technique Works

The concept is straightforward. You use a separate battery charger capable of delivering a brief pulse of higher-than-normal current to shock the dendrite crystals loose inside the battery. The zap only needs to be strong enough to knock off the crystalline dendrite growth. It is meant to be a brief pulse for shock treatment purposes, not a sustained high current flow. If you apply constant high current for too long, it will generate excessive heat inside the battery, which could potentially lead to overheating or even fire. Brief and controlled is the key.

Step-by-Step Revival Process

Step 1: Confirm the battery is NiCad. This technique works specifically on nickel-cadmium batteries. Check the battery label for NiCd, NiCad, or nickel-cadmium markings. Do not attempt this on lithium-ion or lithium-polymer batteries as it could be dangerous.

Step 2: Apply the zap. Using a battery charger that can deliver a brief pulse, connect the dead NiCad battery for just a few seconds. You are not trying to fully charge it at this stage. You are only trying to break through the internal dendrite blockage.

Step 3: Transfer to regular charger. After the initial zap has broken the dendrite crystal formation, there should now be enough conductivity restored for your regular charger to work. Place the battery in its normal charger and let it go through a full charge cycle.

Step 4: Cycle the battery. For best results after revival, fully charge the battery, use it until it is nearly depleted, then fully charge it again. Doing this cycling process two or three times helps recondition the battery and maximize its recovered capacity.

Why NiCad Batteries Are Still Worth Keeping

NiCad batteries may seem like old technology, but they have genuine advantages over newer battery types in certain applications. They can deliver high current output, which makes them excellent for power tools and devices that need sudden bursts of energy. They also perform well in extreme temperatures where other battery chemistries struggle. So do not be too quick to toss them. Revive them first and save both money and environmental waste.

Quick Tips

Do not leave NiCad batteries disconnected for long periods. This is what causes the dendrite growth problem in the first place.

Store NiCad batteries with a partial charge. Not fully charged and not fully depleted.

For more DIY repair content, check out how to do bathtub caulking and rearview mirror repair.

This topic is also covered in detail on handymanfix.com.