# Can we use a capacitor with battery to fast charge it?

Consider this. Many capacitors connected in parallel to an input line, those capacitors are in series connected to battery. Whenever we need to charge, we plug in adapter that charges the capacitors. Since all are in parallel, they charge soon, since being capacitors, can charge faster too. All these capacitors can be connected to a battery in series, so one capacitor when gets depleted, the charge flows from the next capacitor, the capacitor nearest to the battery is fully charged and keeps charging the battery slowly. Will this work?? Ps: the idea is to make fast charging work by using capacitors to hold temporary charge and use it to charge the battery. So battery can be connected in series with capacitors to achieve this?

• no, because to harvest the energy in the cap you have to lower the voltage below what the battery needs to charge. Components in parallel want to have the same voltage. Very quickly the battery and cap will be at the same voltage and nothing else will happen, other than slowly draining the battery by the cap's leakage current. Commented Feb 9, 2021 at 19:47

No, if you pump enough energy into those caps to charge the battery, it will destroy the battery when put into series. Apply 100V to a 12V battery and see what happens.

And even if it did work, you would need MASSIVE MASSIVE caps since capacitors have much lower energy density than the battery. It also doesn't change how fast the battery is charged since the caps have to stay with the battery until it is charged.

• Using a voltage regulator or a adapter? Commented Feb 10, 2021 at 2:10
• @hindisong.cc That's called a battery charger, a terrible, capacitor powered battery charger that still needs to remain connected to the battery until it is fully charged. What you're suggesting is like me throwing a bunch of sandwiches into your back pack and acting as though you ate those sandwiches as quickly as I threw them into your bag. Commented Feb 10, 2021 at 3:14

No, because if all the capacitors are in series, the current through each of them is the same. This means that they are all discharging at the same rate, at the same time.

• Ok, so if we connect the battery and capacitors in parallel? Commented Feb 10, 2021 at 2:06
• @hindisong.cc Maybe, but it's not that easy. As the battery charges, its voltage increases. But as the capacitors discharge, their voltages drop. So you need something to manage the charging of the battery and match the voltages. Commented Feb 10, 2021 at 14:45

To answer this question for yourself, choose some random battery with current technology. Calculate how much energy it can store -- multiplying its nominal voltage by its nominal capacity in ampere-seconds will get an answer that's good to within 10 or 20%.

Now choose some current capacitor technology that has high energy density, and that will charge from 0V to it's rated voltage in whatever time you find desirable (probably electrolytic or a supercapacitor, although supercapacitors tend to have less current capability).

Now figure out how much volume and weight of those capacitors you need to store as much energy as that battery, using $$\w = C \frac{v^2}{2}\$$.

Now compare the weight and size of your battery with the weight and size of your capacitor bank, and you have your answer.