What is the output current of two batteries in series?

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Discussion Overview

The discussion revolves around the output current of two batteries connected in series, particularly when one battery is functioning properly while the other is defective. Participants explore the implications of battery properties, internal resistance, and circuit conditions on the current output.

Discussion Character

  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants assert that when batteries are in series, the same current circulates through them, regardless of their individual conditions.
  • Others question how to define the output current when one battery is healthy and the other is defective, suggesting that the current output may not be straightforward.
  • One participant proposes that if one battery delivers a higher current (e.g., 2A) and the other a lower current (e.g., 0.5A), the output current would be the lower value (0.5A) due to the series configuration.
  • Another participant notes that while the series connection provides a higher voltage, the defective battery may still be able to deliver more current than expected.
  • It is mentioned that the behavior of real batteries is influenced by internal resistance, which complicates the relationship between voltage and current.
  • Some participants emphasize that the output current is determined by the external circuit connected to the batteries, rather than the batteries themselves providing a specific current.
  • One participant argues that the question of differing currents in series is invalid, asserting that two batteries in series must deliver the same current.

Areas of Agreement / Disagreement

Participants generally agree that the same current circulates in batteries connected in series, but there is disagreement regarding the implications of having a defective battery and how it affects the output current. Multiple competing views remain on the topic.

Contextual Notes

Participants express varying assumptions about battery behavior, including the effects of internal resistance and the nature of the external circuit, which may not be fully resolved in the discussion.

hikari1987
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when they have the same properties , the same current circulates in them because they are in series .. but the question is how to define the output current when there are two batteries , one in good health and the other defective so one deliver a high current and the other a lower one ?
thank you for your help !
 
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Hello Ikari, welcome to PF :smile: !

the same current circulates in them because they are in series
still holds !
 
BvU said:
Hello Ikari, welcome to PF :smile: !

still holds !

thank you :D

well actually given the chemical and physical properties of the batteries , the same current circulates in them when they operate at the same conditions , but when for example a battery delivers let's say I=2A and the other I=0.5 , which current would be the output ?

thank you again !
 
It would be 0.5 A according to
the same current circulates in them because they are in series
.

There is a question mark to be placed here: If you put two batteries in series, the combination delivers a higher voltage, so the 'bad' battery doesn't have to "push" that hard, which means it may be able to deliver a bit more current.

Batteries are sold as "voltage providers" (you buy a 1.5 V battery, not a 0.5 A battery).
Ideal voltage providers deliver the nominal voltage, no matter what current is flowing. They don't exist (fortunately -- or there would be a lot more fires).

Our first approximation to describe the behavior of real batteries is to assume there is an internal resistance inside the battery. So if our 1.5 volt battery has to deliver 1 A and the actual voltage provided is 1.25 V we say that the internal resistance takes away 0.25 V at 1 A. Ohm's law tells us the internal resistance must be 0.25 Ω.

Actual batteries don't have such a simple linear behaviour for V as a function of I.
 
Absolutely. A battery provides a certain voltage, say in this case, 1.5 V. If you have two such batteries in series, together they provide 3 V. provided both of them are still alive. It is not they they "give" a certain current. The current depends on the circuit that you connect. If, with the two batteries in series, you connect a 10 ohm resistor, you draw a current of 0.3 A. If you connect a 1 ohm resistor, you draw 3 A. This is assuming that the batteries are ideal, with zero internal resistance. For real batteries, you just add the internal resistance to the outside resistance you connected, in series. If you draw more current by using two small a resistance in the circuit, you just kill the battery sooner.
 
hikari1987 said:
well actually given the chemical and physical properties of the batteries, the same current circulates in them when they operate at the same conditions, but when for example a battery delivers let's say I=2A and the other I=0.5 , which current would be the output ?

The question is invalid.

Two batteries in series will ALWAYS deliver the same current. It's not possible for them to deliver different currents if they are in series.

Two batteries in parallel could deliver different currents.
 

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