MPG Varies Wildy, 2012 Prius

I have a 2012 Prius Three with 140k miles. I have checked the air filters, cabin air filters, auxillary battery, tire pressure, and traction battery using the Dr Prius app. The weird thing is that there are no error codes at all, no lights or anything. The battery check shows no battery errors, and says that my traction battery has 77 percent life left. I think that some of this just may be me being new to hybrids and just the nature of the type of driving that I'm doing, but even then I don't think that the mpg should be this low unless maybe the car's sensors for mpg are off somehow, which I doubt.

I was thinking of having the battery brought to a hybrid specialist, but I don't know if the battery is even the issue here. I was checking the earlier posts about the brakes being an issue with mpg. There was a brake issue noted, but it was repaired before I bought the car. I'm not sure if the EGR system has been cleaned, so that may be an issue I'm just not sure.

Hybrid status monitor shows the gas engine powering the car and the battery very often. The battery discharges very fast and does not hold a charge for long. Other than that I don't have much of an idea to what the issue could be. There is also a sound of a servo moving after the car shuts off. From what I've researched it has something to do with emissions but I'm not sure.

Any and all input/help is appreciated, thank you for your time and just let me know if you'd need any other clarification/info.

- Have you read This Thead Yet?
Yes I have, my driving is very stop and go over short distances. In this case I get terrible mileage (15-25), when I go on the highway I get 44. My mpg on the consumption over time varies wildly too

- What fuel economy are you getting and how are you determining fuel economy? (trip computer or manual calculations)
Car's built in monitor

- What fuel economy are you expecting and why?
At least 40, seems reasonable for this car with age on it

- What are the approximate outside air temps?
80+ F

- How long are your trips?
5-30 mins

How old is your 12v battery? What is the voltage reading of your 12v battery after sitting over night? (Method Here)
Would need to test, had it checked at an auto store and it says 4 years left

Have you had your alignment checked? Any pulling or abnormal tire wear?
Tires are new, haven't noticed any pulling

- How much of it is city vs. highway? Roughly what's the average speed in overall and and of each segment? Is there a lot of stop and go driving?
Tons of stop and go driving, very heavy traffic

- What's the terrain like of your drives? (e.g. flat, gentle hills, steep hills, etc.)
Flat mostly, gentle hills and some very poor roads

- What are your tire pressures?
Specced to the manual

- Is your oil overfilled? (i.e. above the full mark on the dipstick)
Oil is not overfilled

- Make, model, year, engine and transmission of previous car? (e.g. 08 Honda Civic Si 2.0L 4 cylinder, manual transmission) What did you actually get on the same trips/commute? (Please give us actual numbers, not EPA ratings.)
2000 Chevy Malibu , 3.1L V6 Automatic, got about 23 mpg

- What region/state are you in? (if you haven't set your location)
Hawaii

- How are you trying to drive (e.g. trying to stay in electric only?) and how hard are you braking?
Driving as I normally would my other car. Slow braking when needed

- What modes are you using, if any? "normal", EV, power, eco?
Always in eco mode

- Are you "warming up" the ICE (internal combustion engine) by letting it idle after powering on?
I just start it up and go

- Are you driving using D or B mode?
I drive using D mode

- HVAC settings? Are you using the heater, AC, auto mode, etc.? If using auto, what temp is it set to?
AC is mostly at full blast, auto sets it to low. I occasionaly turn it off and see very slight mpg increase

- Are you using the factory tires and wheels? If not, please indicate tire make, model and size (e.g. Goodyear Assurance Fuel Max 185/65R15).
Need to check and add this later

- If reporting a mileage drop, did anything significant change on your car (e.g. accident, hit a curb or big pothole throwing off alignment, oil change/other maintenance/repairs, changed tires or wheels, etc.) or your commute? Not that I know of

 

Highway mpg is 40-44 and city on short trips is 25-30.

Do you mean by getting weak that the battery is reaching the end of its life, or do you just think that it needs to use the recharge? Or is that something you can't really guess witthout looking at it.

 

If you don't mind me asking, how many miles are you on with the battery using the prolong system? I'm debating whether I should put money into an entire new battery or use the Prolong. The Prolong seems like the good idea right here because the only way I can get a battery put in is about 3500, but they say it is lithium ion with 2 year warranty, but I'm not sure if it's worth the investment compared to just using the Prolong and seeing how far it goes.

After using the Prolong, are the results noticable to you, what is the difference in mpg?