Tried seemingly everything to increase MPG -- wondering if I need a new battery

My battery for my 2013 is at 50% too. Have you tried checking your tire pressures? If not, set them to the correct factory PSI. It makes wonder and adds a few more MPG when you have the right tire pressures all around.

Though, when I first bought my car in January, I average 55 MPG, and lately it's been getting 51 MPG now. I think you might be right that it might be because the battery is slowly depleting. Lower your battery, the more times the car needs to start it's gas engine to recharge. That's just my theory though. (I'm not a mechanic)

 

Probably ok, but any recent brake work? You could check how free-spinning the rears are; more info in my signature.

 

Is this car new to you, or have you seen a decrease from a higher number?

 

Exactly what I was going to ask. If this is a change from previous history that might be a very different cause than if you are new to driving a Prius.

 

older batteries are not usually a cause of very low mpg's, but maybe a few, 2-3?

older, worn, neglected enginesand pertinent accessories often are.

 

low hanging fruit

tire brand, model, pressures

12v load test, even though new, you never know

cabin filter

brakes as mentioned above

cleanen the throttle body and maf

does she burn any oil?

have we talked about your driving style?

 

Try cleaning the hybrid battery fan.

 

How much weight are you carrying in your car? Do you have roof rack installed?

 

LRR tires certainly do make a difference, and different models both LRR and non LRR can make a difference as well.
you could try grid charging to rejuvenate the battery

 

Have you replaced both coolants and transmission fluid? Also, use Mobil 1 advanced fuel economy for engine oil. Do this ecu reset as well.

 

When you say “equivalent to another average sized person” how much do you figure that person would weigh: 150 pounds? 200 pounds? 250? 350?
When you say you don’t “hypermile” but don’t lead foot either” from a complete dead stop to 45 mph does it take you a city block to reach it? How far do you coast when coming to a stop? Are you utilizing regenitive braking 100% or stopping pretty quickly?
All of these answers will tell us a lot and lead us to answers that will actually increase your mileage considerably.
A couple of more question, and please be honest, how much do you weigh? How many passengers are you carrying and their approximate weights? Do you run the a/c and keep your headlights on? Do you live in it or use it to camp? Travel through the Rockies or other mountains quite often?

 

OEM rims?

 

Driving style is going to have an impact. Heading to work I average 53mpg according to Trip computer. I decided to drive like I would drive my Buick, which would be considerable more aggressive than the Prius, but not as aggressive as typical driver. MPG dropped to 42MPG. I added in A/C running at higher level, and it was 39MPG. My commute is 80% highway, slightly rolling landscape, with cruise control set at 65 but I set it to 70 on the two MPG tests. Your lower MPG might be from driving like a normal ICE.

 

plugs, coils, injectors, air filter, oil level, throttle body, maf, does she burn any oil?

there's nothing you can test for, you just have to go through each item starting with the easiest, and finishing with the hardest.
the national average is 47mpg iirc, so you're not as far off as you might think. a few for the tires, a few for the battery, a few for the engine, and you're right there.

how are you measuring mpg's?

 

ATF fluid

If you haven't changed ur ATFs, u haven't technically 'tried everything' I've gained up to 4mpg just by changing the ATFs. Also, get a can of fuel treatment. I've gotten 2-3 mpg gain by using fuel system cleaners.