Total lifetime value: A yardstick for comparing batteries

BY SOL JACOBS,
VP and General Manager,
Tadiran Batteries,
www.tadiranbat.com

The low initial cost of a consumer battery is often misleading, as this investment tends to be short lived and carries various hidden costs, including reduced productivity and/or the loss of sensitive data due to unreliable performance or premature battery failure, along with the cumulative cost of continually replacing batteries every 2-3 years, as well as the labor costs associated with battery replacement, which can be substantial if the device is located in a remote, hard-to-access location.

Fig. 1: Superior grade LiSOCL2 battery feature an annual self-discharge rate of just 0.7%/year, and can operate up to 40 years

To maximize the performance of increasingly sophisticated remote wireless devices, design engineers need to choose the ideal power supply based on a variety of considerations, including the total lifetime value of the investment, which requires a solid understanding of the performance differences between consumer and industrial batteries.

Consumer batteries are plentiful and inexpensive, including billions of primary (non-rechargeable) batteries that are manufactured each year to power flashlights, remote controls, and toys.

Likewise, cost considerations drive the procurement of consumer grade rechargeable batteries that are used to power cell phones, tablets, laptops, and other portable and hand-held devices. Since most cell phone contracts allow for an equipment upgrade every two years, and laptop/tablet devices become rapidly obsolete, it makes sense for the device manufacturer to specify an inexpensive rechargeable battery that will last approximately 5 years and 500 full recharge cycles.

Meanwhile, we are seeing rising demand for industrial devices bound for remote locations where ac-power is not available, thus necessitating a self-contained power supply for the entire operating life of the device, which can be as much as 40 years. For industrial applications such as automotive toll tags, GPS tracking devices, scientific and oceanographic instruments, remote sensors, automatic utility meters, process controls, and other M2M devices, the choice of power supply is driven more by the total lifetime cost, especially when the labor cost of battery replacement far exceeds the cost of the battery itself.

Certain applications are also totally unsuited for consumer grade batteries due to their unreliable performance in extreme environmental conditions. For example, wireless sensors that monitor frozen human tissue or organs being transported through the cold chain need to withstand temperatures as low as -80°C. Bobbin-type lithium thionyl chloride (LiSOCL2) cells are ideal for such an environment because the chemistry is non-aqueous. On the opposite side of the spectrum, down-hole drilling often involves temperatures of up to +150°C, a requirement uniquely served by bobbin-type LiSOCL2 batteries.

Comparing primary batteries
Alkaline cells are readily available and extremely inexpensive, but have drawbacks such as low voltage (1.5 V), a limited temperature range (-0°C to +40°C), a high annual self-discharge rate that reduces their life expectancy to 2 to 3 years, and crimped seals that are prone to leakage and corrosion. See Table 1 for a comparison of some primary battery cell chemistries.
Consumer primary lithium cells are relatively inexpensive, available in either 1.5  to 3 V, and were designed to deliver high pulses needed to power a camera flash. These batteries have several limitations, including a narrow temperature range (-20°C to +60°C), a high annual self-discharge rate, and crimped seals that are prone to leakage and corrosion.
Lithium thionyl chloride (LiSOCL2) cells are ideal for wireless applications that require long-term power, especially in extreme environments. Bobbin-type lithium thionyl chloride (LiSOCL2) chemistry is preferred because it offers the highest capacity and highest energy density of any lithium chemistry, along with an extremely low annual self-discharge rate (

Table 1: Comparison chart of some primary battery chemistries
 
How a bobbin-type LiSOCL2 battery is manufactured can significantly impact its performance. For example, an inferior quality LiSOCL2 battery may deliver 10-year operating life with an annual self-discharge rate of 2 to 3% per year, while a superior grade LiSOCL2 battery can feature a much lower annual self-discharge rate of just 0.7% per year, permitting maintenance-free operation for up to 40 years. Bobbin-type lithium thionyl chloride batteries can also modified using patented hybrid layer capacitors (HLCs) or other means to deliver the high pulses required for powering advanced communications.
 
Consumer rechargeable batteries have evolved
Consumer rechargeable battery technology is improving, and is becoming increasingly cost competitive. This evolutionary curve began with the invention of the Nickel Cadmium (NiCad) battery, which is large, has low energy density, and suffers from “memory effect” whereby a battery that is not fully depleted cannot be fully recharged. Nickel-Metal Hydride (NiMH) batteries eliminated the “memory effect” problem common to NiCad batteries, however, NiMH batteries suffer from a high annual self-discharge rate, thus eliminating the potential for extended storage life.
 
Consumer grade lithium ion (Li-ion) batteries have grown in popularity due to their high efficiency and high power output. The most popular type of Li-ion cell, the 18650, was developed by laptop computer manufacturers as an inexpensive solution that could last approximately 5 years and 500 full recharge cycles. Consumer grade Li-ion cells experience a gradual degradation of the cathode, making these battery less receptive to future recharging, which reduces their total lifetime value. These batteries also have crimped seals.
 
The emergence of slim profile smart phones and tablet computers led to the broad scale commercialization of thin lithium polymer batteries, which are reasonably inexpensive, but have several drawbacks, including a limited service life, performance issues at extreme temperatures, and a tendency to swell in size over time.

Industrial grade rechargeable Li-ion batteries offer long-term value
Rapid growth in remote wireless applications, including energy harvesting devices, has created strong demand for an industrial grade rechargeable lithium battery, which led to the introduction of TLI Series Li-ion batteries. These industrial grade rechargeable batteries offer a high lifetime return on investment because they can operate maintenance-free for up to 20 years and 5,000 full recharge cycles. TLI Series batteries also feature very low annual self-discharge rate, the ability to be recharged in extreme temperatures (-40° to +85°C), the capability to deliver up to 15-A pulses from an AA-sized cell, and a glass-to-metal seal to withstand harsh environments.

Innovative breakthroughs involving ruggedized rechargeable Li-ion batteries and bobbin type LiSOCL2 cells allow design engineers to weigh the low initial investment cost of consumer rechargeable batteries against the greater total lifetime value offered by industrial grade batteries.