# What are you really measuring as a battery discharges?

• ptownbro

#### ptownbro

Think for example a phone or any devices that shows the amount of battery power is left. It shows it as a graphic where you can deem whether it's full, 3/4 full, 1/2 full, 1/4 etc... or shows the actual percentage. What is that measure really showing you? Voltage? Amp hours left (which is the capacity I think)? And, how is it calculated?

As a battery discharges the voltage drops under load. This is mostly due to internal resistance increase.
http://www.mpoweruk.com/soc.htm discusses it. It's possible to monitor this externally.

But. most LI-ion batteries have an internal monitoring circuit that reports charge and discharge data back to the operating system. This is best because the data is so battery dependent.

## What are you really measuring as a battery discharges?

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:

## 1. What is the voltage of the battery?

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.

## 2. How much current is being produced by the battery?

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.

## 3. What is the state of charge of the battery?

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.

## 4. How much energy is being delivered by the battery?

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.

## 5. What is the internal resistance of the battery?

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.