To fix up or trade in. Should I fix up my 2004 with 140k? Should I replace the hybrid battery?

I believe @Texas Hybrid Batteries repairs combo meters.
@TMR-JWAP or @ericbecky could help you determine the state of the hybrid battery. Assuming you are in the continental US the most economical DIY solution is the kit of new cells from @2k1Toaster for $1600 shipped with a 2 year warranty. Details are in my signature but they are backordered until April due to popularity.

 

Let it go.. If you like GenII there are 2008/2009 in market at much lower price now.. Prius monopoly seems to be fading away very fast and used PrII prices are coming down to earth...

 

If you're not putting enough miles on the 04 to justify insurance costs, then I'd sell it privately, but the fact that you're thinking on trading it in on another new car leads me to believe that you're not especially worried about money.

Your call.

I would NEVER trade a car in on another car.
If you think that you need to scratch the PHEV itch, then fix the items that need immediate attention (tires, exhaust) and leave replacing the traction battery for the next owner or when it fails. I would then sell the car privately.....maybe even in this forum.
TIME is your greatest asset for this issue, and you can use it to save a little money in this case, although a 14-year-old car is probably 3/4 of the way through its service life - and so we're not talking about a lot of money for somebody who has a 2016 in the garage and is salivating over a 2018.
Me?
I'd keep the 04, but then again $1000 means a lot more to me than it might to you, and that represents my estimation of how much you could save in selling rather than trading a car in.....in this case.

"Peppy" isn't the tell of the tape for Prius health, but rather fuel efficiency is.
If your MPGs start dropping off, then it's time to look into your car's health, and chances are it will not even then be traction battery related.
Those batteries are getting to be fairly cheap, remanufactured and they're very easy to replace.
I would not worry about it until I had to.

Good Luck!
Let us know what you decide.

 

I'd fix the issues if cheap to repair, and then sell private party. Trading in tends to eat 1-2k of the value. If your time is worth more then that, then trade it in, and get what you want

 

I am of the opinion that the big ticket items like cars should be used till they drop. That is the sane environmental approach. By using the car till its last mile you are not creating demand for a new car to replace it. This really makes a difference in reducing your footprint on this planet. If a car like a Prius was actually designed to run for 300K and more than 15 years, then that's a very good thing. Fixing the minor problems is not that big a deal and requires relatively little impact on your wallet and environment. Fight the urge to get the lates consumer gadget/car and you are halfway there to setting an example to the next generation of people, hopefully. There are so many other things you could spend the money and energy on than a shiny new car which would do exactly what your '04 does. Gets you from place to place in relative comfort. Just my opinion. I am not an environmental nazi, just have this world view, is all. Do what you want, obviously.

 

fix and keep, 2004 is a beast.

 

This sounds similar to me so I suggest that you look at used plug-in's, they are a tremendous value right now.

 

What would the trade in value be?

If the OP doesn't know, one way to get an estimate would be to drive it to a local Carmax and see what they would offer.

 

Does it have side airbags LOL I'll buy it. Depending on the price. I'm in the market for a cheap prius for commuting purposes. Prefer to deal with forum guys than CL.

 

I don't think there is a trade in value for this 2004. I would CL it for $1K-2K depending on where you at in US. There are more suckers like you and me once were wanting to jump in to hybrid lifestyle that are looking for challenges that go along with owning hybrid vehicle.

Or have a project and convert it to small pickup truck with rear-bumper sticker indicating "Small truck big prius".. Note, this is my original and no one should take credit for it.

 

Hybrid demo derby looks fun. Apparently the Prius is a beast!