As a scientist, I understand that this is a common question when it comes to batteries. The five most frequently asked questions about what we are measuring as a battery discharges are:
The voltage of a battery is the amount of electrical potential difference between the positive and negative terminals. As a battery discharges, the voltage decreases due to the depletion of its chemical energy.
The current of a battery is the rate at which electric charge flows through it. As a battery discharges, the current decreases due to the reduction of its chemical reactions.
The state of charge is the amount of remaining energy in a battery, expressed as a percentage of its total capacity. As a battery discharges, the state of charge decreases.
The energy delivered by a battery is calculated by multiplying the voltage and current over a specific period of time. As a battery discharges, the energy delivered decreases due to the decrease in voltage and current.
The internal resistance of a battery is the opposition to the flow of electric current within the battery itself. As a battery discharges, the internal resistance increases due to the depletion of its chemical energy.