Accurately Calculating Battery Life

In summary, the conversation discusses ways of accurately measuring battery life for a listening device using 2 x AA batteries. The use of discharge curves and individual cell characteristics are mentioned, as well as the impact of temperature on battery life. The conversation ends with the speaker expressing gratitude for the helpful ideas.
  • #1
big_tobacco
6
0
:confused: Hello

Could you tell me is there a way of accurately measuring battery life? Basically I have a listening device, it requires 2 x AA batteries, say 2400mAh each (so...4800mAh in total).

I am aware you can ‘estimate’ battery life by determining the device’s current consumption and then calculating against the battery(s) mAH rating, however this assumes the supply voltage remains constant.

I have measured the device as having an on-load voltage of 3.04V, and an off-load voltage of 3.08V.

Also I have found the minimum total voltage required to power the listening device is 1.35 V. (0.67 V per battery)

With this information how could I find out how long the device will run for by cross-checking it with a manufacturer's ‘Discharge Characteristics chart’.

I would be most appreciative if anyone could help.

Kind regards

Lee
 
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  • #2
big_tobacco said:
:confused: Hello

Could you tell me is there a way of accurately measuring battery life? Basically I have a listening device, it requires 2 x AA batteries, say 2400mAh each (so...4800mAh in total).

I am aware you can ‘estimate’ battery life by determining the device’s current consumption and then calculating against the battery(s) mAH rating, however this assumes the supply voltage remains constant.

I have measured the device as having an on-load voltage of 3.04V, and an off-load voltage of 3.08V.

Also I have found the minimum total voltage required to power the listening device is 1.35 V. (0.67 V per battery)

With this information how could I find out how long the device will run for by cross-checking it with a manufacturer's ‘Discharge Characteristics chart’.

I would be most appreciative if anyone could help.

Kind regards

Lee

Welcome to the PF. What do you mean by on-load and off-load? If you mean a changing load on the battery supply voltage, those should be in currents, no?

You estimate battery life using the discharge curves you mention. If the load current is varying, you need to go back and forth between the different load curves, ratioed by whatever the duty cycle of the load is.

Also, the batteries are considered used up typically when their voltage falls to something like 85% of their starting voltage (varies by type of battery), so you are not going to get much extra life between there and the low 0.67V per cell that you mention in your post.

Can you post a link to the discharge curves for the battery that you want to use, and say more about the current consumption of the load and the duty cycle and frequency of the changing load current?
 
Last edited:
  • #3
I think he means the open-circuit voltage is 3.08V. When he connects his load, the voltage goes down to 3.04V.

- Warren
 
  • #4
You can't. Any discharge curves you obtain from the manufacture will merely represent a sample, at best. They will not necessarily reflect individual cell characteristics accurately.
 
  • #5
big_tobacco said:
Basically I have a listening device, it requires 2 x AA batteries, say 2400mAh each (so...4800mAh in total).

Just to point out, when you connect batteries in serial the voltage adds but the Ah remains the same. When they are in parallel the voltage remains and the Ah adds. So your two AA batteries are 2400mAh at 3v.
 
  • #6
negitron said:
You can't. Any discharge curves you obtain from the manufacture will merely represent a sample, at best. They will not necessarily reflect individual cell characteristics accurately.

Agreed. For awhile I was a product engineer at a company that made consumer products with the batteries installed at the factory. I was supposed to write a spec. for testing the battery because customers were complaining the batteries were DOA. I called the battery manufacturer up to get their spec. and was surprised to find out there was none.

One of the problems is that batteries deteriorate very rapidly when exposed to temperatures over 40 C. That's an uncontrolled variable during shipping, both from the manufacturer to the factory and from the factory to the store. How hot do you think semi-trailers get inside during shipping in summer? In short, lifetimes can vary tremendously from battery to battery.
 
  • #7
Fantastic, to be honest everyone has given me some very useful ideas - I shall definitely keep you posted!
 

What factors can affect the accuracy of battery life calculations?

Some factors that can affect the accuracy of battery life calculations include the age of the battery, the type and quality of the battery, the device usage patterns, and environmental conditions such as temperature and humidity. These factors can vary greatly and impact the overall performance and lifespan of a battery.

How can I accurately calculate the battery life of a device?

The most accurate way to calculate battery life is to measure the actual power consumption of the device and the capacity of the battery. This can be done through specialized equipment or by using software tools that track the power usage of the device. It is also important to take into account any external factors that may affect battery life, as mentioned in the previous question.

Can battery life be accurately predicted?

While it is possible to estimate battery life based on previous usage patterns and the specifications of the battery and device, it is not always accurate. This is because battery performance can vary greatly depending on a variety of factors and can degrade over time. It is always best to measure battery life rather than rely on predictions.

Why is it important to accurately calculate battery life?

Accurately calculating battery life is important for several reasons. It helps users manage their device usage and avoid unexpected shutdowns. It also allows manufacturers to design more efficient devices and batteries, leading to better performance and longer lifespan. Accurate battery life calculations can also inform decisions about battery replacement or upgrading to a newer device.

What are some common misconceptions about battery life calculations?

One common misconception is that a higher battery capacity always means longer battery life. However, the actual battery life depends on the power consumption of the device and not just the capacity of the battery. Another misconception is that charging a battery to 100% will always result in longer battery life, but this can actually cause degradation in some types of batteries. Additionally, battery life can vary greatly depending on usage patterns and external factors, making it difficult to accurately predict.

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