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Battery Know-what/why (Article 2)
Naphtal Haya
September 19, 2023
This is the second article of the Battery Know-what/why Series. See the first article here if you missed it: https://rechargeable.beehiiv.com/p/battery-knowwhatwhy. This article covers 6 more prevalent terms used to describe the construction, performance and operation of a battery: charge, discharge, C-rate, capacity, current and potential difference. You have probably come across some or all of these terms in various contexts. Let us see if we can gain a better understanding of them. The use of a water tank analogy will aid the explanation of these crucial terms.
Water tank to battery cell analogy
#7 Charge: the process via which electrical energy is added to a battery cell.
#8 Discharge: the process via which the energy stored in a battery cell is released.
#9 C-rate: refers to the rate of charge or discharge. The unit of C-rate is C and the quantity is a reciprocal of the duration it takes to fully charge / discharge a battery cell. For instance, a battery cell that requires 4 hours to get fully charged has a C-rate of 0.25C.
#10 Capacity:
Know-what: refers to the quantity of electrical charge (electrons) stored in a battery cell. Capacity is measured in ampere-hours (Ah).
Analogy: think of a water tank - capacity is analogous to the volume of water in the tank.
Know-why: impacts charge/discharge durations. Higher capacity translates to longer charge/discharge durations for a fixed rate of charge/discharge.
This article covers 6 very prevalent terms used to describe the performance and operation of a battery: charge, discharge, C-rate, capacity, current and potential difference.
#11 Current:
Know-what: refers to the rate of flow of electrical charge and is the quotient of capacity (Ah) and duration of charge or discharge (h). Current is thus measured in amperes (A).
Analogy: think of a water tank - current is analogous to the volume of water added/removed from the tank per second.
Know-why: Current rating indicates the rate at which a battery cell’s capacity (electrical charge) can be replenished/consumed.
#12 Potential difference (voltage):
Know-what: refers to the electric force/pressure that exists between the positive electrode (cathode) and the negative electrode (anode) that drives the flow of electrons from one terminal to the other. Potential difference (commonly called voltage) is measured in volts (V).
Analogy: think of a water tank - potential difference is analogous to the height of the tank. The greater the height of the tank, the higher the rate of water ejection.
Know-why: influences power and energy ratings of a battery cell (see below).