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I am working with CR-P2 batteries. I have a few questions that I am trying to answer. I would appreciate if anyone kindly help me with these questions. Thanks in advance.

  1. I have found in google two different types of CR-P2 batteries from different vendors. One group has 1500 mAh capacity and another group has 1400 mAh capacity. Most of them claims 10 years battery life. Why these two battery capacity numbers are significant? How significant is the capacity difference of 100 mAh?

  2. When we draw large pulse current from the battery (let's say 3500 mA) it generates heat. I am assuming it is because of the resistor inside the battery that heats up. Is there any other reason? It causes battery faster degradation. Why does that happen?

Thanks again for your help.

Best, Niloy

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  1. The mAh is a unit for measure of energy dished out by 1 ampere flowing continuously for 1 hour. It's a measure of the capacity and strength of battery over time. So 100 J of energy should count when used for a low resistance load, but for high resistance load that seems to be your case, it doesn't matter too much in a practical sense. For the battery life expectancy, that obviously depends on the quality of materials and manufacturing process used, so if you wish to investigate, you'll have to cut open one and do some chemical analysis.

  2. If there is a resistor along one of the terminals, it means the resistivity in ohms might be too high for what you're loading the battery with. My advice, try doing a circuit analysis of the battery, the resistor, and your load, that way you can vary the resistance of the resistor and optimize how much power is consumed by the resistor as the current increases. You might decide to take out the resistor if you wish, but doing so will increase the voltage of the battery relative to the voltage with resistor in it. Also ordinarily, batteries tend to heat up due to cumulative energy losses over time as large current is dished out, so you can do nothing to that, unless you'll tradeoff reducing the resistance of your load. As for the degradation issue, there might be numerous causes, like your load, or battery quality, but I don't think the heating up has anything to do with that. Anybody else might have a better answer to that question.

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Response to Question 1

In low power applications, mAh helps determine the battery life. When determining the battery life for an application the mAh advertise in battery specification sheet is important, but more importantly how the mAh are derived. Different regions in the world use different criteria to determine the mAh. For example USA markets will use around 20mA load to derive the mAh for a battery where as the same manufacture will use a 30mA load for outside of USA. As a result the same battery will be listed as 1500 mAh battery for the US market and 1400 mAh for markets outside the US. Therefore if mAh is important for the application a dialog with the battery vendor will be very beneficial.

Below is a discharge curve vs service life chart for a Duracell Ultra 223 CRP2 battery.

Discharge Curves for Duracell Ultra 223 CRP2 battery

From the above chart it note that the service life varies based on the discharge current. Therefore it is important to review the specification sheets to understand the battery capabilities as it relates to the specific application.

Response to Question 2

Technically there is no resistor inside the battery, but components use in battery contribute to a total effect resistance, also known as internal resistance. The two primary contributing components are electronic resistance and ionic resistance. Electronic resistance is made of material such as metal covers and material used to make contact. Electrochemical factors such as electrolyte conductivity, ion mobility and electrode surface area make up the ionic resistance component. Ionic resistance occurs slowly and effect on effective resistance varies base on various factors.

Note: CR-P2 batteries are made by combining two CR123 batteries.

References:

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