BU-104a: Comparing the Battery with Other Power Sources

One hears of wonderful improvements in battery technologies, each offering distinct benefits, but none providing a fully satisfactory solution to all of today’s energy needs. Though the battery has many advantages over other energy sources, it also has major limitations that need addressing.

Energy storage

Batteries store energy reasonably well and for a long time. Primary batteries (non-rechargeable) hold more energy than secondary (rechargeable) and the self-discharge is lower. Lead-, nickel- and lithium-based batteries need periodic recharges to compensate for lost energy. (See BU-802b: What does Elevated Self-discharge do?)

Specific energy (capacity)

Compared to fossil fuel, the energy storage capability of the battery is less impressive. The energy by mass of gasoline is over 12,000 Wh/kg. In contrast, a modern Li-ion battery only carries about 200 Wh/kg; however the battery has the advantage of delivering energy more effectively than a thermal engine. (See BU-1007: Net Calorific Value)

Responsiveness

Batteries have a large advantage over other power sources by being ready to deliver on short notice – think of the quick action of the camera flash! There is no warm-up, as is the case with the internal combustion engine (ICE); battery power flows within a fraction of a second. In comparison, a jet engine takes several seconds to rev up, a fuel cell requires a few minutes to gain power, and the cold steam engine of a locomotive needs hours to build up steam.

Power bandwidth

Most rechargeable batteries have a wide power bandwidth, meaning that they can effectively handle small and large loads, a quality that is shared with the diesel engine. In comparison, the bandwidth of the fuel cell is narrow and works best within a specific load. So does the jet engine, which operates most efficiently at a defined revolution-per-minute (RPM).

Environment

The battery runs clean and stays reasonably cool. Most sealed cells have no vents, run quietly and do not vibrate. This is in sharp contrast with the ICE and large fuel cells that require compressors and cooling fans. The ICE also needs air intake and provision to exhaust toxic gases.

Efficiency

The battery is highly efficient. Li-ion has 99 percent charge efficiency, and the discharge loss is small. In comparison, the energy efficiency of the fuel cell is 20 to 60 percent, and the ICE is 25 to 30 percent. At optimal air intake speed and temperature, the GE90-115 on the Boeing 777 jetliner achieves an efficiency of 37 percent. The charge efficiency of a battery is connected with the ability to accept charge. (See BU-808b: What causes Li-ion to die? under Coulombic Efficiency)

Installation

The sealed battery operates in any position and offers good shock and vibration tolerance. Most ICEs must be positioned in the upright position and mounted on shock-absorbing dampers to reduce vibration. Thermal engines also need an air intake manifold and an exhaust muffler.

Operating cost

Lithium- and nickel-based batteries are best suited for portable devices; lead acid batteries are economical for wheeled mobility and stationary applications. Price and weight make batteries impractical for the electric powertrain in larger vehicles. The cost of drawing energy from a battery is about three times higher than getting it off the AC grid. The calculation includes the cost of the battery, charging it from the grid and budgeting for an eventual replacement. (See BU-1006: Cost of Mobile Power)

Maintenance

With the exception of watering of flooded lead batteries and exercising NiCds to prevent “memory,” rechargeable batteries are low maintenance. Service includes cleaning the corrosion buildup on the outside terminals and applying periodic performance checks.

Service life

The rechargeable battery has a relatively short service life and ages even if not in use. The 3- to 5-year lifespan is satisfactory for consumer products, but this is not acceptable for larger batteries. Hybrid and electric vehicle batteries are guaranteed for 8–10 years; the fuel cell delivers 2,000–5,000 hours of service, and depending on temperature, large stationary batteries are good for 5–20 years.

Temperature extremes

Like molasses, cold temperatures slow the electrochemical reaction and batteries do not perform well below freezing. The fuel cell shares the same problem, but the internal combustion engine does well once warmed up. Fast charging must always be done above freezing. Operating at a high temperature provides a performance boost, but this causes rapid aging due to added stress. (See BU-502, Discharging at High and Low Temperatures)

Charge time

Here, the battery has an undisputed disadvantage. Lithium- and nickel-based systems take 1–3 hours to charge; lead acid typically takes 14 hours. In comparison, filling up a vehicle with fuel takes only a few minutes. Although some electric vehicles can be charged to 80 percent in less than one hour on a high-power outlet, Li-ion batteries get stressed on ultra-fast charges. (See BU-401a: Fast and Ultra-fast Chargers)

Disposal

Nickel-cadmium and lead acid batteries contain hazardous material and cannot be disposed of in landfills. Nickel-metal-hydride and lithium systems are environmentally friendly and can in small quantities be included with regular household items, but authorities recommend that all batteries be recycled. (See BU-705: How to Recycle Batteries)