In order to design a battery based on existing lead acid chemistry and technology, but having superior performance in terms of longevity, the Caterpillar engineering team needed to have a thorough understanding of the failure modes and performance limitations of current technology.  There is, to put it bluntly, lots of room for improvement.  The following is a short summary of the main performance shortcomings, or “bottlenecks” of existing lead acid batteries.

• Life:  Lead acid batteries suffer from a limited useful life due primarily to two factors:  Corrosion of the positive grid and sulfation on the negative grid.
  
  
• The corrosion failure mode is primarily due to the fact that the positive battery plates are required to perform their function as “electron collectors” in an incredibly harsh, acidic environment.  What’s more, batteries are frequently required to operate in high-temperature conditions, which have the effect of accelerating corrosion.  To mitigate the effects of corrosion, battery manufacturers have focused their research efforts on developing corrosion-resistant lead alloys and grid manufacturing processes.  Although improvements have been attained in this manner, corrosion remains one of the most common failure modes of lead acid batteries.
  
  
• Sulfation failures result from a lead acid battery being kept in a discharged state for a period of time.  In this situation, the lead sulfate formed in the normal chemical discharge reaction re-crystallizes and hardens.  This non-conductive lead sulfate blocks the conductive path required for recharging.  Once they’re in this crystalline state, the sulfate crystals are very difficult to convert back to the charged lead and lead oxide required to produce the battery’s energy-producing chemical reaction.  Even a well-maintained battery will, over time, lose some of its capacity due to the continued growth of large sulfate crystals that are not entirely reabsorbed during the charging cycle.  The sulfate crystals are also larger in volume than the original paste, so they can actually mechanically deform the plate or grid by pushing the material apart.  Sulfation is a common problem in recreational vehicle applications where extended off-season storage leads to dead batteries that will not accept a recharge.
  
  
• Cycle Life:  Cycle life is a term that refers to the number of deep discharges that a battery can endure without significantly diminishing its useful life.  As users have become more familiar with rechargeable batteries in cell phones and laptop computers, they have become comfortable with bringing these batteries down to an almost totally discharged state and bringing them back to full capacity with a recharge of just a few hours.  In contrast, conventional lead acid batteries, because of inherent design and utilization limitations, are only capable of handling discharges down to 20 to 30 percent of full capacity.  The number and frequency of these deep discharges can lead to a drastic reduction in the battery’s overall life span.  A motorist who forgets to turn his or her headlights off and has to have the battery recharged because it’s totally dead most often never realizes that the battery has suffered a deep-discharge “injury” that will significantly shorten its useful life span.  Many new products that have historically used lead acid batteries are now being requiring a significant increase in cycle life.  A notable example is the hybrid electric vehicle, which requires high-rate discharges at mid to low state-of-charge conditions.  Such conditions are a nightmare for designers of conventional lead acid batteries, as their products simply do not possess sufficient overall longevity under such conditions.  This has left car companies no alternative but to go with much more expensive alternatives such as Nickel-Metal Hydride, and even to begin experimentation with Lithium Ion technology.
  
  
• Vibration:  Having worked for years at CAT, the premier manufacturer of heavy equipment, Kurt Kelley was particularly sensitive to developing a design that could minimize the adverse effects of vibration and rugged use.  Conventional lead grids generate a great amount of “back and forth” force when subjected to vibration and jarring.  Although steps (such as anchor-bonding) have been taken by battery manufacturers to reduce these effects, the root cause is the mass of the heavy lead grids.  Batteries subjected to continuous, severe vibration literally tear themselves to pieces, internally, over time.
  
  
• Recharge Time:  Typically a lead-acid battery product will require a recharge time significantly longer than the advanced materials seen in portable products. A complete charging of a lead-acid battery, such as found in electric vehicles, can take from 8 to 16 hours.  In the case of Uninterrupted Power Supplies (UPS), a rapid charge rate is essential to quality performance, as well as reducing the related capital expenditures for back up equipment while charging takes place on initial batteries put into service.
  
  
• Size and Weight:  Although lead-acid batteries are the cheapest energy storage products in the world to manufacture, the extensive use of lead gives them an exceptionally large footprint and weight. Again, like other performance aspects of this industry’s products, this limits their form factors and overall utilization in new product designs. In addition, a traditional lead battery plate (there are over 100 of these in a typical automotive lead acid starting battery) on average only utilizes 30% to 40% of its surface area over the life of the battery. This creates even more inefficiencies of power-to-weight ratios.

Although lead acid battery technology has had many decades of ongoing development, new demands are stretching its fundamental capabilities to the limit.  Notwithstanding its relatively low cost, many industries, such as the automotive industry, have been forced by these limitations to turn to much more expensive technologies that hold significant issues of their own.  The timing is certainly right for a technology that breaks through the above-described constraints and enables new levels of performance, reliability, and affordability from well-proven lead acid chemistry.