12v battery, mpg tracker--normal or Mouse?

Betty* is a 2016 Prius V, bought used 3 yrs ago, with 117,000 mi; I need to to last twice that, like her mama, Stella, my Corolla wagon. No serious issues, I don't think, but two kinda wonky things.

The first is the 12 volt battery. It's at least years old, so yeah, could be nearing end of life. 19 out of 20 times the car starts just fine. Then I get the "auxiliary battery doesn't have enough juice," message. But once, after getting the message, when I was getting ready to jump it, it started up on its own. That was weird. It will start on its own for weeks, even when I forget to turn ac, etc off before turning off. Then it might need jumping on/off a couple times, then good for weeks. Auto zone tried to test it, twice. The first time, maybe a year ago? they kept saying they couldn't get a read, then did and it was fine. This time they gave up without getting a read, and it started just fine.

So I started watching the little diagram of where power us going, that shows engine, then hybrid battery, then what I assume is this one??? It never shows blue bars all the way to the top. Even when driving, it will show power going from this one to the hybrid or engine, with blue bars disappearing, then going back up. I know on a non hybrid, the battery should be charging, not discharging, unless alternator issue, so not sure what this means???

Then there is the main and trip odometer mpg data. The main one, with lifetime miles, usually stays pretty much the same all the time, but lately has varies from 25pmg to 47 mpg. Same with trip odometers.

So the two together made me wonder...about mice. I did get a mouse in it on a camping trip. (Ironically, I was parked next to another Pius V and owner was saying she had a mouse problem; I think one of hers jumped ship.) I had signs in the glove box, and later in a bag with hiking snacks, but could not catch in trap, nor hear sleeping in car. My two cats show a lot of interest in the car...but always did.

Soooo...my questions are:
- whatdya think is going on with the battery?
- could it have a slightly chewed line somewhere?.
- if so, how do you find it test? t
- best way to test battery?
- is it ok to keep jumping it until dies completely? (kinda waiting for the fall battery sales)
- is the mpg variation stuff normal, or could there be a wire issue on that, too?

* She is named Betty after Queen Elizabeth, for longevity; Betty White for playful spirit; and Betty, a friend's French bulldog for being ..we just everything.

 

I intend to, but $200 is a lot of money for some of us (ok, me), so was hoping for a sale, which are usually in the fall, AND if there is a wire issue, I want to know before I get a new one. So, any way to test for that?

 

Um, I thought I posted this to the Prius forum; If you dislike Priuses, why are you here?

Please note that I did not ask about whether to get rid of this car, just about whether I was dealing with a regular maintenance issue, or a mouse issue--which the Corolla also fell prey--and how to determine which. Sorry if you missed that.

I'm also sorry if you had an issue with your Prius, but hopefully you're mature enough to understand that there are always a few underperforming individual vehicles-- plus none of us here can ascertain if you were a contributing factor to its issues. So please, don't project your problem onto the millions of highly satisfied Prius owners of ~17 years.

Moreover: I wanted a wagon, because I am a car camper with a large dog. (Following guidance on this forum, I took out back seat and built a platform with storage space, which has given me far more luxurious accommodations than the Corolla ever did). Toyota was not selling Corolla wagons when I needed to replace the 95 with 350k. The Matrix was not appropriately ergonomic for me. But most importantly, many of us--especially those of us who are environmental scientists--know the dismal facts about climate change and feel a personal responsibility--as everyone should-- to reducing our carbon footprints, and are doing our part by buying hybrida and EVs. I could not afford an EV; it was difficult enough to find a Prius owner willing to part with one...which again speaks toowner satisfaction.

Perhaps you should request PriusChat open a secrion for Dissatisfied Owners to share your opinions and advice?