Batteries and Supercapacitors

I am hobbyist trying to understand what is possible and feasible with the use of batteries and supercapacitors.  My current power supply consists of 6, 18650 3.7V 3200mAh connected in a 3x2 configuration giving me an output of 9600mAh at 7.4V. It will power my device for about 31 hours at 2.5Wh. My goal is to prolong run time of my device without adding more batteries. M questions are as follows:1)Can I prolong battery life by adding a capacitor/supercapacitor to the circuit? My thought is that the capacitor/supercapacitor would charge/trickle charge the battery pack thus extending the life OR be a supplement/additional power supply. The capacitor/supercapacitor would be charged instantaneously by 120VAC.When the battery pack is depleted it would be removed and charged via a wall outlet.

2)Can the power supply be only supercapacitor without the battery pack and be charged instantaneously with 120VAC?

Is it possible? Is it feasible from a size and cost standpoint? Thank you for your help in advance.

Assuming that you are not charging the supercaps periodically during operation, this will not be a good solution.

Chances are you want to maximize the energy density in Ah/Kg for the battery pack (power/weight). The 18650 batteries will have significantly higher energy density than the super caps do, so you would be better off adding more 18650 batteries than adding super caps.

The super caps do not charge instantaneously, but they charge very quickly compared to Lion batteries. Super caps have an internal resistance which limits max charge rate and many also have a rated maximum charge/discharge rate which must be limited by an external circuit.

Thanks for your answer.

Randal,
It appears you are using LCO (Lithium Cobalt Oxide) batteries.
The voltage range for these will be 2.8VDC (at 0% SOC) fully discharged
to 4.2VDC (at 100% SOC) full charged. So for your 2S3P pack you built its parameters are:
Voltage range: 5.6 - 8.4VDC
Capacity: 9.6Ah
Energy: 71Wh
If your device is pulling 2.5W continuously then this gives you a run-time of 28.4 hours.
18650 LCO off the shelf cells capacity will vary quite a bit especially if they are 2nd or 3rd tier supplies.
You are wanting more run-time (battery life relates to how long the battery can used before replacement). Super caps do not increase your system capacity, which you want. They are used to handle large current surges which would damage or destroy the LCO cell. If your application has a continuous power draw then increasing your capacity would be answer as Dean noted.
Make sure you are getting to the maximum voltage with your charger. Also if you do not have a cell balancing circuit tied to your pack then your capacity is limited to your weakest cell. The more cells you put in parallel (increasing capacity) the more balancing you will have to do. With batteries it is all about managing current distribution both in the charge and discharge.

Jeff,

Thank you for your detailed response. I appreciate you taking the time help me. Have a great day.

Randal