Battery Know-what/why (Article 3)

This is the third article of the Battery Know-what/why Series. See the first two articles here if you missed them: https://rechargeable.beehiiv.com/p/battery-knowwhatwhy; https://rechargeable.beehiiv.com/p/battery-knowwhatwhy-article-2. With the 6 terms covered herein, this article continues the exploration of three fundamental questions: What is the construction of a battery? How is battery performance measured? How does a battery operate? This week’s battery terms are configuration, energy, power, P-rate, gravimetric energy density and volumetric energy density - all derived from the quantities displayed in the figure below.

#13 Configuration

• Know-what: refers to the number of cells connected in series (positive to negative terminal connection) or in parallel (positive to positive and negative to negative terminal connections) in a battery module. An example of a battery module configuration is 3P2S which means 3 parallel connections of 2-cell series connections.

• Know-why: series connection increases a battery module’s voltage while parallel connection increases capacity.

#14 Energy

• Know-what: refers to the product of capacity and potential difference (voltage). Energy is measured in watt-hours (Wh).

• Analogy: think of a water tank - energy is analogous to the product of the volume of water in the tank and the pressure at which it is ejected.

• Know-why: impacts usage duration. Higher energy rating translates to longer charge/discharge durations for a fixed power rating.

#15 Power

• Know-what: refers to the rate at which a battery cell’s energy level is increased (charge) or decreased (discharge). Power is measured in watts (W).

• Analogy: think of a water tank - power is analogous to the product of the volume of water added/removed per second and the pressure at which it is ejected.

• Know-why: impacts load size - battery power has to match load power.

#16 P-rate:

• Know-what: refers to the quotient of a battery’s rated power and rated energy. The unit of P-rate is P. For instance, a battery of 500 W power rating and 1000 Wh energy rating has a P-rate of 0.5P.

• Know-why: impacts load size - battery power has to match load power.

#17 Gravimetric energy density:

• Know-what: refers to the quotient of energy rating and mass of a battery cell. The unit of gravimetric energy density is watt-hour per kilogram (Wh/kg).

• Know-why: a higher gravimetric energy density translates to fewer battery cells for the same energy requirement.

#18 Volumetric energy density

• Know-what: refers to the quotient of energy rating and volume of a battery cell. The unit of volumetric energy density is watt-hour per liter (Wh/L).

• Know-why: a higher volumetric energy density translates to fewer battery cells for the same energy requirement.

References

1. https://www.eptsensor.com/info/what-is-tank-level-indicator-and-ultrasonic-li-83789407.html

2. https://www.power-sonic.com/blog/how-to-connect-batteries-in-series-and-parallel/