A Look Into Battery Definitions

1 October 2014

A Look Into Battery Definitions

Understanding battery definitions is very important. Batteries come in all manner of forms: large, small, heavy-duty, light-duty, different brands and more. Distinguishing the batteries is not as easy as naming a dog. First, they will share similar characteristics. Second, they will work in similar manner. The battery may come as a single cell, or connected in series. For instance, series connection powers electric vehicles and also uninterruptible power supply (UPS) units. A high capacity battery may deliver low power while a low capacity battery may come with high cranking capacity as high as 300 amps.

The battery systems used in renewable energy sources such as wind and solar are very large. For instance, a wind farm delivering 30MW (megawatt) will have 15MW storage batteries. One megawatt will cater for a large Walmart store or 50 homes. This is equal to 20,000 starter batteries. The cost of such a unit will be approximately $10 million. The following are the main ways in which batteries are defined:

Chemistry

Chemistry is simply the chemical elements that make up the battery. The main compounds are nickel, lead, and lithium. Each material will require different handling, charging and disposal. Batteries may share similar characteristics. These include; cranking capacity, amperes, voltage and more. However, using a charger meant for a different battery will affect the performance and durability of the battery.

Voltage

The voltage imprinted on the battery is the nominal charge. This is the charge the battery will have when not in use or being charged. A user should make sure the value matches that of the charger or device. The voltage that is read when the battery is being charged or under load is known as CCV (closed circuit voltage). The value will vary depending on load and charge. The OCV (open circuit voltage) on a fully charged battery will exceed the nominal charge slightly.

Capacity

Capacity indicates the energy or power in the battery. It is measured in ampere-hours (Ah). The capacity of the battery is usually overrated by manufacturers. A 100 Ah battery will last longer than a 50Ah battery when powering a similar device. But, it will take longer to charge. You can go for a large capacity battery as long as the voltage remains the same.

Cold cranking amps (CCA)

CCA or cold cranking amps refers to the battery’s ability to crank in very cold temperatures. The standard is set at delivering at least 1.2 volts per cell or 7.2 volts for 30 seconds in temperatures of 0 degrees Fahrenheit or -18 degrees Celsius (centigrade). The higher the CCA the better the battery will crank at this extremely low temperatures.

Specific/ Gravimetric power

Specific/gravimetric power refers to the load capability. Or in simple terms, the amount or quantity of current (amperes) produced by the battery. Improved loading capability is achieved by reducing the resistance inside the battery. This is seen in batteries used in power tools which have low capacity (specific energy) but high specific power.

Specific energy density

Also known as gravimetric energy density, specific energy density measures the energy produced in comparison to its weight or volume. It is rated as Wh/kg or Wh/l. A battery with high specific energy may suffer from low load capacity. This is mostly observed in alkaline batteries. Some batteries behave like super capacitors whereby they have high load capacity despite their low specific energy.

C-rates

C-rates define the rate at which a battery charges or discharges. At 1C, the discharging rate will be equivalent to the indicated Ah rating. At 0.5C the value will be halved while at 0.1C the battery will lose a tenth (10%) of the marked value. When it comes to charging, a battery marked 1C will charge in approximately an hour, a 0.5C will require 2 hours, while it will take 14hours for a battery marked 0.1C.

Load

Load is the amount of energy drawn from the battery. High load means the battery’s peak is almost being reached while low load indicates only a fraction is being used. Under high load the battery will get drained much faster compared to low load. The physical work of load is measured in Watt-hour (Watt-hour).

Volt-amps (VA)/Watts

Energy or power drawn from the battery is measured in VA (volts-amps) or watts (W). VA is the noticeable power while Watt is the ideal or real power. The values will be similar in loads with pure resistance such as fluorescent lights and inductive motors. In less resistance, the values will vary. This is due to the drop in the power factor (pf). The ideal value is 1.0; however, resistance may bring it down to 0.7 or 70.