November, 2011
Inspection News and Views from the American Society of Home Inspectors

Keeping Your Batteries Charged


Battery Fact: NiCad batteries currently are the most popular for power tools, but technology cannot increase their power without increasing their size. Since they already are heavy and bulky, the next level in batteries is the Lithium-ion battery.

In the 1970s, the movie “The Graduate” made the word “plastics” famous. Today, in the world of tools, the “one word” might be “cordless.” In the movie, plastics translated to phony or superficial. The same might be said of cordless tools when they first came on the market in the late 1970s. Basically, they were a flashy gimmick that couldn’t compete with corded tools in performance.

Today, cordless tools are widely used by professionals, including home inspectors and DIYers. The transition from gimmick to common usage occurred, in part, because of improved rechargeable batteries. Understanding these batteries can help ensure your lightweight, take-anywhere cordless tool is ready to go when needed instead of sitting on a charger.

Volts and amps

Whether the cordless tool has the more common Nickel-Cadmium (NiCd) battery or the newer Nickel Metal Hydride (NiMH) battery, the higher the voltage, the better the performance in doing heavier projects such as cutting thicker wood and driving bigger bits. Nevertheless, most homeowners do not need the power provided by an 18- or 24‐volt tool. A 12- or 14.4‐volt tool usually will do the job, with the added benefit of being lighter and less cumbersome.

Amps are a consideration for tools with a NiCd battery. A higher amp rating means a cordless tool can operate for a longer period of time. Amp‐Hour ratings can be 1, 2, 2.8 or even 3.

Getting the most out of a NiCd battery

Storing a NiCd battery in a high temperature area or overcharging it will cause it to fail prematurely. Additionally, using the cordless tool when encountering resistance produces heat and shortens battery life.

Simply recharging a battery reduces its life since the process generates unwanted heat. Basic chargers provide a continuous trickle charge. That means even when the battery is fully charged, it still has energy trickling into it. The unwanted energy produces heat that reduces the battery’s life. Some chargers have a thermal switch that automatically shuts off when it senses overheating.

Smart chargers

State‐of‐the‐art “smart” technology in chargers is available, costly and usually found with professional-grade tools. Microprocessors in these chargers can sense the temperature of the battery and operate accordingly. For example, putting a cold battery into a charger can damage or even destroy it. But the smart charger can slowly ramp up the charge prior to hitting full steam. Smart chargers also can sense when a warm battery is inserted and wait for it to cool down before starting to charge.

According to Gary Katz in the December 1999-January 2000 issue of Fine Homebuilding, ‘Higher Voltage Batteries Have Shorter Lives.” Manufacturers estimate battery life along these lines: 1,000 to 1,300 charges for a 9.6‐volt battery; 800 to 1,000 charges for a 12‐volt battery; 650 to 800 charges for a 14.4‐volt battery and 500 to 800 charges for an 18‐volt battery.
But remember, as previously stated, heat is a battery’s worst enemy and will affect longevity. That, along with how the tool is used and under what conditions, determines battery life. What’s more, the final charges will have less run time than earlier charges.

Although newer, better grade “fast” chargers sense that the battery is full and shut down to reduce overheating, each cell in a battery accepts a charge differently. Cells that are not equally charged reduce battery life. For that reason, many manufacturers recommend that after every eight to 10 charges, the battery be left in the charger for approximately six hours to charge all the cells equally.


Early rechargeable batteries developed a memory, which meant if you didn’t fully charge a battery each time you put it into the charger, you would reduce the battery amps and runtime. That is no longer applicable to today’s rechargeable. Today, after a battery is broken in, you probably shouldn’t completely drain it. Doing so weakens the weaker cells faster and they may not be recoverable.

Barry Murphy of “Batteries Plus” suggests most new rechargeable batteries be fully charged before use. Then, run the battery completely down the first few times you use the tool to fully imprint the battery memory. To retain full memory, it doesn’t hurt to completely run down NiCd and NiHM batteries every five to seven uses and then recharge fully. After that, you can use them any way you want. Most manufacturers recommend you recharge the unit when performance drops. Do not keep a battery in a charger unless it is a smart charger.

Running life increases

Have you noticed a longer running time for cell phones, laptops, some high‐end power tools? That’s because of the new Lithium-ion (Li‐ion) batteries. This newest technology is longer-running, lighter, smaller and even has more power. These batteries should be stored in a semi‐discharged state and not left on a charger between uses. One Li‐ion cell can produce 2 1⁄2 times the power of a NiCd cell. Expect to see a lot more tools, toys and anything cordless using this technology in the immediate future.

Don’t throw in the trash

Finally, never dispose of old batteries by throwing them in the trash. They’re bad for the environment. Drop them off at a battery recycling center. Or, better yet, “Batteries Plus” can rebuild used tool batteries for half the cost of new replacement batteries.

Battery Tips
  • Never put a cold, warm or hot battery into a charger. Wait until the battery is at room temperature.

  • Don’t abuse a cordless tool by pushing too hard or using dull blades and bits, causing it to overheat and prematurely drain the battery.

  • Avoid storing NiCad or NiMH batteries in the charger, even though most newer chargers drop down to a trickle when the battery is fully charged.

  • It is not necessary to store batteries in the refrigerator. All batteries should be stored in a cool, dry environment.

  • Never store batteries in your car or truck when it is extremely cold or hot outside.

  • Top off batteries overnight every three to four charges.

  • Recycle all rechargeable batteries; they pose an environmental hazard.

  • Never interchange chargers between battery types (e.g., do not use a NiCad charger with a Li-ion or NiMH battery.)

  • Replace all batteries when a toy or battery-operated device runs down. Mixing old with new shortens the life of the newer batteries.

  • Disconnect the battery cables to stored lead-acid batteries (motorcycle, lawnmower, marine, etc.). The battery

  • should be stored in a cool, dry environment. Every six to eight weeks, recharge the battery with a maximum 2-amp trickle charge or use a battery maintainer.

  • Keep the battery terminals on an automotive battery clean and tight; most newer ones are sealed and maintenance-free.
If your car battery has removable caps or plugs, you should check the water level every two to three months. Remove the caps in all the cells. The fluid should completely cover all the plates in the battery. If not, add distilled water only. Do not overfill.

A version of this article was originally published in the Eccentric newspaper chain in Southeast Michigan, February 2011.