# When two capacitors are connected in parallel, do they drain battery quicker?

My question is actually my answer to a question I asked myself i.e 'how does potential difference remain same for both capacitors which are connected in parallel, and not get distributed'

When 2 capacitors (lets say, of same capacitence 1F) are connected to a battery of 1V(a source of charges), then the capacitors take some energy from the battery and put some charge inside them (Q=CV=1Coulomb for both capacitors). Which means the battery now has less energy.

Now, if those 2 capacitors were a part of seperate circuits with same volatages, they would still aquire same charge (Q=CV=1 Coulomb) as they did when they were connected in parallel. But in this case the individual batteries( which are part of 2 seperate circuits with a capacitor each) will only loose lower energy each.

So, hence I answer my question as: potential difference across capacitors in parallel remains same becase the battery has a huge supply of energy that will be supplied at some fixed voltage, hence both capacitors can suck up the energy they want from this continously supplying source(but with fixed oomph).

Hence I conclude, the battery with 2 capacitors in parallel will drain out faster than a battery with individual capacitors(considering we charge the capacitors many many times, causing the battery to loose the energy).

Now does this all make sense or its just baloney?

Now does this all make sense or it's just baloney?

It's just baloney.

Batteries don't "lose" charge when they charge a capacitor. Batteries simply move electrons from one plate making it positively charged to the other plate making it equally negatively charged. The net charge on the combination of the two plates of the capacitor is the same (zero) before and after charging so no charge has been "supplied" by the battery.

The positive terminal of the battery pulls electrons off of the capacitor plate connected to it, making that plate positively charged.

At the same time the negative terminal of the battery pushes the same number of electrons onto the capacitor plate connected to it, making that plate negatively charged.

In order to move the charge the battery needs to do work agains the attraction and repulsive forces. The voltage across the battery equals the work per unit charge in Joules/Coulomb the battery does to move the charge from one plate to another the plates. For a 1 volt battery and 1F capacitor, that's 1 Joule of work.

A mechanical analogy may be helpful.

A water pump provides mechanical force to move water through a piping system. The pump does not supply water, it just provides the needed mechanical force to move the water already in the pipes.

The electrical analogy is a battery provides the necessary electrical force (due to the electric field produced by the battery) to move the freely mobile charge already in the circuit (producing current). The battery does not supply the charge, it just provides the electrical force needed to push the charge in the circuit.

Hope this helps.

• Thanks Bob, that was really helpful, i cant believe i missed the fact that capacitor doesnt take charge from battery. Commented Apr 26, 2022 at 12:59
• Can you comment of this paragraph, "So, hence I answer my question as: potential difference across capacitors in parallel remains same becase the battery has a huge supply of energy that will be supplied at some fixed voltage, hence both capacitors can have charges accumulated in them from this continously supplying source(but with fixed oomph)." Commented Apr 26, 2022 at 13:11
• @RohitShekhawat In view of the fact that you now realize batteries don't "supply" charge but do work to separate charge, I don't understand why you are still talking about the battery having a "huge supply of charge". Commented Apr 26, 2022 at 13:30
• In the main post I wrote 'huge supply of charge'. but in above comment I rephrased it to 'huge supply of energy'. That is, I corrected the mistake you are reffering to. I hope there are no other mistakes in my understanding now, thatnks for helping. Commented May 18, 2022 at 11:20
• @RohitShekhawat That's good. But why don't you revise your question to replace huge supply of charge to huge supply of energy? Commented May 18, 2022 at 11:57

Like Bob D's answer indicates, despite the understandably confusing language, a "charged" battery and a "charged" capacitor are both neutral as a whole, in the sense that they have no net positive or negative charge. This doesn't change as a battery supplies energy to a capacitor. That said, as this is happening, a certain amount of charge flows through the battery, which is what is what we refer to when we speak of the charge supplied by the battery. A battery has a limited capacity, which is the amount of charge it can supply. The capacity also depends somewhat on how fast you discharge the battery (i.e. the current).

To answer the question in the title, yes. It takes more charge (or energy) to charge multiple capacitors up to some voltage than one capacitor, so after you are done charging them, the battery will have drained more. In addition, the battery actually drains "faster" when charging multiple capacitors in parallel in the sense that, at any given time, the battery will have supplied more charge (or energy). There is also the fact batteries discharging at higher currents have a reduced capacity.

• "A battery has a limited capacity, which is the amount of charge it can supply". I think you may want to clarify this by saying the battery has a limited amount of energy it can supply not charge. Specifically, a limit amount chemical potential energy. Just a suggestion, not a criticism. Commented Apr 20, 2022 at 22:22
• @BobD I hear you and I don't disagree, but the capacity of a battery normally refers to how much charge it can supply, e.g. in units of Ah. The energy it can deliver is still limited of course and is closely related to capacity.
– Puk
Commented Apr 21, 2022 at 1:01
• I'm sorry Puk but a battery is not a source of charge. It is a source of electrical potential energy to move charge that is already in the circuit. What you are saying is simply wrong. I will leave it at that. Commented Apr 21, 2022 at 1:22
• @BobD I'm not saying a battery generates charge or transfers net charge to a load. I think my answer makes that clear as well as what I mean by "charge supplied". Battery capacity specified in charge is established terminology.
– Puk
Commented Apr 21, 2022 at 1:27
• I am only suggesting the phrase "supply charge" tends to reinforce the OP's misconception. A battery no more supplies charge than a water pump supplies water. The both supply the energy to move something already there. If it were me I would say "move charge". It is only a suggestion, but hey it's your answer and you own it. Commented Apr 21, 2022 at 12:14