BY CHRIS G. GREENE AND PATRICK DURHAM | Energy Hazards
THE HOLIDAY SEASON is officially upon us. Soon, we will each find ourselves searching for that perfect gift for our family, friends, and loved ones. When I was a kid, the holiday season meant family, food, and a Christmas tree surrounded by presents. In 1979, this 10-year-old kid got the first of many battery-operated toys. I remember my father scrambling to get all the batteries together and load them into each toy. None of the batteries looked the same: big ones, small ones, and all different colors. Watching my father work, I wondered, How does he know which batteries to use? They all look different to me. So I asked him, “Dad, how can you tell which ones go where?” “They’re all pretty much the same, son,” he said. “If they fit in the toy, then they’re going to work.”
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In 1979, that answer was just fine by me. Today, however, I would respectfully reply, “Batteries are not like LEGO, Dad. Just because they physically fit in the space doesn’t mean they’re the correct batteries.”
The small toy/tool consumer battery landscape has changed substantially over the past 45 years. Gone are the days of “If it fits, it will work.” The size and shape of a battery today are not an indication of consistent chemistry and corresponding voltages. They vary, and when multiple batteries are required to reach the voltages needed to power that device, consistent battery chemistry becomes particularly relevant.
Over the past 100 years, we’ve had access to many battery types and chemistries. However, in this article, we will limit the content to those most prevalent in the toys and hand tools market.
Alkaline: Nonrechargeable
This is the cornerstone of the nonrechargeable primary cell for tools and toys, the one we all grew up using. Its name is an indication of the chemical features of this battery. An alkaline battery uses a basic (alkaline) electrolyte medium of potassium hydroxide (KOH). Potassium hydroxide is the preferred electrolyte for these cells due to its compatibility with most electronics, favorable conductivity features, and low freezing point. Alkaline battery cells offer good thermal stability, which equates to consistent performance even under the most extreme cold or hot weather conditions. They are inexpensive, are portable, and today most have a shelf life of more than 10 years. They are considered environmentally low impact and easily pass the Restriction of Hazardous Substances (RoHS) European Union (EU) electronic materials directives.
RoSH: Restrictions of Hazardous Substances
RoSH is a European directive that limits the use of hazardous substances in electronics. The testing process ensures that products comply with these regulations and have minimal effects on the natural environment. Heavy metals and chemicals, such as lead, mercury, cadmium, hexavalent chromium, and bromine, all carry considerable restrictions in Europe due to the RoSH directive. Initially, the RoSH directives only applied to the EU, but many states have since adopted similar constraints.
Nickel Cadmium (NiCd): Rechargeable
For most of us who are over 50, this was our first exposure to a small portable cell that could be recharged. Now, I realize that even back then lead acid batteries were common. But, for a kid, we didn’t have much use for it, and it certainly never made its way into a kitchen junk drawer. In 1980, the NiCd battery meant never having to buy new batteries just to throw them away after each use. Forty years ago, “throwaway” was the term we used for alkaline cells. However, those NiCd rechargeable batteries never really lived up to the hype. They did not have the energy density of an alkaline, which meant they did not last as long. Also, they were plagued with high passive discharge characteristics. So even if that cell was fully charged on Sunday morning, by Friday it may have lost as much as 30% of its charge, even if it was just sitting on the counter.
This battery is also plagued by high internal resistance and diminished cycle count, and its memory effect can be severe. To maintain the energy capacity of this cell, it must be periodically fully discharged and cycled. However, the upside is that NiCd batteries are some of the most robust and abuse forgiving cells on the market, even for today’s standards. They are one of only a few battery chemistries that can truly handle the rigors of rapid charging with minimal degradation to the cell. This is one of the things that keeps this cell in such high demand. Unfortunately, due to the cadmium, the NiCd cell is considered toxic to the environment—so much so that in 2006 the EU banned its use except in the narrowest of applications, such as aircraft. Today, due to these same toxicity concerns, the global market use of NiCd batteries is restricted to specialty applications.
Nickel Metal Hydride (NiMH): Rechargeable
The NiMH battery cell represented an evolution in the NiCd cell. First introduced to the consumer market in 1989, it was available in AA, AAA, and other sizes and featured greater specific energy than its predecessor, which resulted in a longer-running battery cell. The NiMH is less prone to memory issues and is considered an extremely robust cell. The departure from cadmium in its chemistry resulted in a more environmentally friendly battery for consumers. Nonetheless, it shared some of the same evolutionary gaps that were present in the NiCd cell. For example, the NiMH cell has an elevated passive discharge rate. Some references have this at 20% within the first 24 hours and 10% per month thereafter, which makes it one of the highest drop offs for this type of cell. Even so, the NiMH was a mainstay for tools, toys, and even hybrid electric vehicles (HEVs) for many years. Additionally, up until just a few years ago, this was the standard format cell in portable radios for the fire service, which has recently transitioned to lithium-ion cells.
Lithium Metal: Nonrechargeable
In 1989, the first consumer-commercial application of the lithium metal “AA” battery hit store shelves. It boasted superior power, longer run times, and the longest shelf life for a cell of this size. However, it was markedly more expensive than its counterpart, the alkaline cell—as much as five times more expensive for the same “AA” cell. Where the lithium metal battery excelled was in expensive products, like cameras, and medical equipment, such as pacemakers with “lithium-iodine” chemistry, where it is the preferred choice today. In smoke detectors, the term “maintenance free” for 10 years implies the use of a lithium-metal battery.
Lithium-Ion: Rechargeable
The lithium-ion cell is considered the mainstay for today’s rechargeable widgets and gadgets. From toys to tools to computers, and even EVs/HEVs, the lithium-ion rechargeable cell is unparalleled. Today, it would be unusual to find any hand tool or toy that isn’t powered by lithium-ion batteries. They boast the highest energy density and one of the lowest passive discharge rates for any rechargeable battery. They can be optimized for high energy demand tools like hand drills, which require high specific power. They can also be designed with high specific energy characteristics for use in devices with low energy demands, which need to run for extended periods without the need for frequent recharging. However, the lithium-ion optimization formula is dynamic and ever evolving. For example, the 18650 cell is one of the most common lithium-ion batteries available to date. It is quite literally the workhorse of the portable tool and electric mobility world. This cell (18650) is available in many chemistries, each with different voltages. This use of varying chemistries is a form of optimizing the battery for a specific use. In a perfect world, a battery would provide for all the following:
- High specific energy.
- High specific power.
- Extended shelf life.
- Low impact on the environment.
- Fast charging ability absent degradations.
- Affordability.
- High cycle life.
Unfortunately, increases in one characteristic often result in a decline in another. It’s a kind of trade-off. Devices that need fast, high-power delivery are more likely to use reflective chemistries, such as nickel manganese cobalt (NMC). This was once the preferred chemistry of power tools, electric mobility, and electric powertrains; however, due to concerns with how cobalt is mined, this chemistry is on the decline.
Static Voltage
The 1.5v standard for single-cell designs in AA, AAA, C, and D batteries has not translated to the rechargeable space that is heavily influenced by the plethora of lithium-ion chemistries. When I was a kid, the voltage for most all the batteries needed to run my toys was static at 1.5v, with the exception of the 9v battery. This is why my father said, “If it fits, it will work.” He was correct for 1979; however, today, in the rechargeable space, the voltage can vary within similar cell formats. We have to look no further than the 18650 cell to see how different they can be. With voltage variations between cells, it becomes critical that they match when used in the same device. And, for that matter, they need to match the charging device.
For example, if that electric drill is designed to be powered by 5 cells, each with a voltage of 3.8v, and you purchase an aftermarket battery pack that contains cells with voltages of 3.0v, you may have some real problems. Not only will this diminish the drill’s performance, but when you dock that power pack in the charger, you run the risk of overcharging those cells. This can, and has, led to fires.
Forty years ago, we did not have this issue because the voltage for the most common cells was static at 1.5v. Today, you must consider the voltage when you purchase replacement cells and battery packs for the most common rechargeable devices. My advice: Stick with the manufacturer’s recommendations for battery cells, battery packs, and charging devices.
Rechargeable Devices: Design Safeguards
Today, most rechargeable devices do not require that the cells be removed and placed into an actual charging platform. The device is simply plugged into a charging block. This passive safeguard helps to ensure that the cell designed for that specific device, a nonmatching cell does not replace the device’s original battery management system. However, there are some devices that require the removal of the batteries for charging purposes. For example, many of today’s flashlights come with removable lithium-ion cells and an additional charging station for the batteries. This can prove problematic if the manufacturer batteries are replaced with batteries that do not meet the same specifications.
Today’s Battery Malfunctions Can Be Severe
A close look at two of the most common batteries in the rechargeable and nonrechargeable spaces, the 18650 and AA alkaline cell, reveals some stark differences between the hazards posed when they fail.
The lithium-ion 18650 batteries and alkaline AA batteries look similar, but they have substantial differences in their chemistry, energy density, and failure mechanisms. Further, when they malfunction, the outcome is considerably different (photo 1). Lithium-ion 18650 batteries are known for their high energy density, storing up to three times the amount of energy of an alkaline AA battery. That’s a lot of energy in a relatively small package. When a lithium-ion battery fails, the release of this stored energy can be sudden and violent, leading to catastrophic events, such as explosions or fires. The internal chemistry of a lithium-ion 18650 battery is another fundamental factor influencing its propensity for a violent malfunction. Under normal conditions, lithium-ion batteries are stable, but if they become damaged, experience a short circuit, or are exposed to excessive heat, the internal temperature can rise rapidly. The damage will cause the internal separator to fail, leading to a phenomenon known as “thermal runaway.” During this failure process, a significant amount of toxic and flammable gases, such as hydrogen, carbon monoxide, and other hydrocarbons, is released. These gases can quickly ignite as the chemical reaction heats the cell to around 1,2000F. The battery’s temperature continues to rise uncontrollably, often leading to the ignition of surrounding materials. Adjacent cells that are thermally impacted may also begin to fail, which is a phenomenon known as cell fire propagation. As the failures cascade through each cell, the probability of quenching such a fire becomes improbable.
In contrast, alkaline batteries function using a more stable and lower-energy chemistry. Even when an alkaline battery fails, the amount of energy released is significantly lower, resulting in less dramatic outcomes. While a failing alkaline battery may release hydrogen, it is insignificant when compared to that of a lithium-ion battery of similar size. A failing alkaline battery cell may release a corrosive substance that can damage the device it is powering, but the reactions involved do not typically produce flames or explosive gases.
Small Battery Disposal
With the exception of alkaline and zinc- carbon batteries, federal law requires that all batteries be recycled—and for good reason. Recycling provides opportunities to recapture battery material for other purposes. However, the primary reason for recycling is to ensure the health of our natural environment. For example, batteries that contain lead, mercury, and cadmium are classified as persistent bioaccumulative toxins (PBTs). A PBT is a toxic chemical present in the environment that can accumulate in people and other animals. PBTs are resistant to natural environmental breakdown and easily spread throughout the ecosystem. This is exactly how you end up with elevated mercury levels in your body if you consume contaminated fish.
As importantly, lithium-ion batteries are particularly troublesome for our landfills, solid waste transfer, and recycling facilities due to their propensity to catch fire. Improperly discarded lithium-ion batteries have been the number one cause of fires in these facilities for nearly a decade. So, resist the temptation to toss those batteries into the trash or your household recycling bin. Take a moment to identify the battery chemistry and check your local battery recycling laws for the state in which you reside. The Environmental Protection Agency is a good resource forfederal laws applicable to battery recycling expectations.
Is the Nonrechargeable Battery Becoming Obsolete?
Absolutely not! There are simply too many advantages to having readily available battery power that isn’t dependent on when it was last charged. That lithium metal nonrechargeable cell can literally sit in a junk drawer for the better part of a decade and retain more than 95% of its original energy capacity. No rechargeable formatted cell is ever going to match that level of dependability when it’s coupled with absolute neglect.
Additionally, not every device can be conveniently recharged. Consider the cardiac pacemaker battery, which is powered using nonrechargeable cells and lasts more than 10 years. Portable power is situationally dependent; therefore, there will always be a place for both formats of battery energy.
Authors’note: Thanks to Isidor Buchmann, Battery University, for contributing content to this article.
CHRIS G. GREENE is a captain (ret.) with the Seattle (WA) Fire Department and a national speaker on energy response hazards. He is the creator of Seattle Fire’s Energy Response Team and assisted in designing its “Energy One” response apparatus. He is a contributing author to Fire Engineering for energy emergencies and creator of the “Lithium-Ion Revolution” teaching platform. He was the 2017 Seattle Fire Officer of the Year and keynote speaker at the Washington State Energy Hazards and Lithium-Ion Battery Symposium. Greene is a technical panel member for FSRI’s Safety of Batteries and Electric Vehicles.
PATRICK DURHAM is a captain and training officer in the Troy (MI) Fire Department. He is a mechanical engineer, engaged in cutting-edge automotive industry projects. Notably, he has been involved in designing innovative multi-material battery structures for EVs. Drawing from more than 15 years of combined experience as a firefighter and an engineer, Durham has developed specialized training courses for firefighters focusing on various technical aspects, including the specific challenges associated with responding to incidents involving EVs. Durham is also a member of the Technical Panel for Fire Safety of Batteries and EVs at the FSRI, where he contributes his expertise to advance the field of fire safety in the context of emerging battery technologies and EVs.
