Lithium ion batteries have entrenched themselves in our everyday lives. From cell phones to laptops to cameras to passenger vehicles, lithium ion batteries have transitioned from “future technology” to technology of today. Lithium ion technology has significantly evolved in the last decade and is now a viable option on fire apparatus. Before we get into why lithium ion may make sense on your next apparatus, let’s discuss what a lithium ion battery is and how it differs from a traditional lead acid battery.
LITHIUM ION VS. LEAD ACID
Every battery is composed of chemicals that create a reaction that allows the storage of electrical energy. Lead acid is of course named after the lead plates and acid inside the battery. Like lead, lithium is a natural metal element. Lithium has been used in watch batteries since the 1970s. However, plain lithium is unstable, which prevents recharging. This is the reason why watch batteries are disposable. In order to maintain stability while charging, research found that using lithium-derived ions created a stable rechargeable battery with the energy density characteristics of elemental Lithium. This resulted in lithium ion batteries. The lithium cathode defines the characteristics of the battery and is paired with other elements to optimize functionality. There are many lithium ion chemistries, but common battery types are lithium cobalt oxide, lithium manganese, or lithium iron phosphate.
Lithium Iron Phosphate is commonly considered the most stable, or safest, of the lithium ion chemistries. It will not provide the absolute pinnacle of charge, discharge, and power density specifications but will provide all the characteristics desired in a lithium ion battery in the safest possible package. The infamous 2013 lithium battery fire on the Boeing Dreamliner used lithium cobalt oxide because of the need for peak performance. For fire apparatus, safety and reliability are always the top priorities, which is why lithium iron phosphate is the recommended chemistry and available from many manufacturers.
We can now discuss the key characteristics that make lithium iron phosphate batteries desirable in certain applications.
DEPTH OF DISCHARGE
A typical lead acid battery is not intended to be discharged beyond 50 percent of its amp-hour (Ah) capacity. That means a 100-Ah group 31 should only be drained to around 50 Ah prior to charging. Deeper discharging will cause a substantial reduction in battery life. Furthermore, lead acid batteries operate with lowering voltages and diminished performance as the battery discharges. This can negatively affect the connected devices. The harsh electrical environment on a fire apparatus frequently requires the batteries to discharge greater than 50 percent and maintain peak performance. This is the reason many departments change batteries out every year or even more frequently.
A lithium iron phosphate battery can handle a depth of discharge down to 80 percent of its rated Ah capacity. That is a 60 percent increase in usable energy over a traditional lead acid battery. During a discharge cycle, lithium ion batteries have very minimal voltage drop. Where a lead acid battery may drop to 11.5 V or lower when fully discharged, a lithium ion at the same discharge level will maintain very close to the fully charged voltage (around 13.5 V). This facilitates peak performance of connected devices throughout the battery discharge cycle. Lithium ion batteries can also be charged at a much faster rate than a traditional lead acid. Depending on the manufacturer’s recommendations a typical lithium iron phosphate battery can be charged eight to 10 times faster than a lead acid. This metric is critical for the emergency industry when time plugged into shore power can be limited. It’s also ideal for maximizing the available output on the high amperage alternators frequently found in fire apparatus.
A “cycle” is the combination of a discharge and recharge event that is over five percent of the battery’s Ah capacity. A standard flooded lead acid battery has a typical cycle life of 250 cycles. A high-performance Absorbent Glass Mat (AGM) battery has a cycle life of around 500 cycles. For both a flooded lead acid and AGM battery, those life cycles are based on up to 50 percent depth of discharge. If you discharge to 80 percent or more, you can reduce the cycle life by more than 50 percent based on the frequency of discharge or age of the battery. In comparison, a lithium iron phosphate battery has a typical cycle life of 3,500 cycles down to 80 percent depth of discharge. That is 3,000 more cycles than a high-performance AGM with 60 percent more usable energy.
How do these numbers impact a real-world fire apparatus? Assume the average urban/suburban department in North America cycles its batteries once per day (overnight charging). Flooded lead acid batteries would last less than a year, high performance AGMs would last a little more than one year, and lithium iron phosphate batteries would last nearly 10 years.
Cost is, of course, the first thing that comes to mind when it comes to lithium ion. In a group 31 size, a lithium ion battery typically costs seven times more than a traditional lead acid battery and three times more than a high-performance AGM. These increases have been the primary barrier from departments adopting lithium ion. Considering the example above, lithium ion has 10 times the lifespan of a traditional lead acid and seven times the lifespan of a high-performance AGM. That means the initial price point of the battery pays for itself in the first six years of service and costs less over the 20-year average lifespan of a typical fire apparatus. That doesn’t take into account the cost of labor to replace batteries or the impact of taking the vehicle out of service.
A majority of fire apparatus use a single bank of batteries for the entire vehicle, which means the engine is starting off the same batteries that run all the other electrical devices. Virtually no lithium ion battery has a cold cranking amp rating, so it’s difficult to know if there is enough power to start a large diesel engine. This is primarily because the technology is still new, and testing hasn’t caught up with the demand. A vast majority of lithium ion batteries require circuit protection in the form of a fast-acting fuse. So even if the lithium battery has enough power to crank an engine, there may not be a commercially available fuse large enough to support the amperage required to start a large diesel engine. Ultimately, lithium ion batteries may not make sense for starting engines with high cranking amperage requirements.
Lithium ion batteries may not make sense for starting all engines, but like any new technology advancements are already taking place. The racing industry is currently testing lithium ion for engine starting to reduce weight. Outside of engine starting, lithium ion is certainly a good option for auxiliary batteries in a multibank system or as an alternative to diesel generators. Both applications require deep discharging, long cycle life, and rapid recharging, which are the defining characteristics of lithium ion. Increasing requirements for idle mitigation in fire apparatus will also drive more vehicles to require alternatives to fossil fuel power. Several FAMA member companies offer lithium ion idle mitigation solutions as part of their product options, and further advancement will likely only increase the number of lithium ion batteries on apparatus in the near future.
FAMA is committed to the manufacture and sale of safe, efficient emergency response vehicles and equipment. FAMA urges fire departments to evaluate the full range of safety features offered by its member companies.