We have an old Prius we rarely used that has needed a new battery for...I'm too embarrassed to say. It's more of a project than it sounds like for several reasons.
First, without a working battery, the rear hatch does not open normally. The only way to open it is to crawl through the interior into the back, then find a small opening with a manual release, then figure out how to get it to actually release. And if you don't apply upward force on the door while you do that, it will immediately latch itself closed again. Adding to the fun, the release is below the rear deck, so you have to lift it out of the way, when you would prefer to be sitting on it. It is awkward.
Second, getting to the battery requires you to remove a lot more than anyone would reasonably expect. To take out the small section of floor above it, you first half to remove the main floor and the storage tray underneath it. Then you finally have access to the battery. You have to unscrew the contacts and the bracket the holds it in place down inside a narrow well that's just big enough or the battery. It does not easily fit ratchets or even screwdrivers at the angles where you need them. It is also awkward.
Third, it's a simple thing, but lifting a car battery out of a narrow hole when you have nothing to hold onto is surprisingly difficult. The battery that was in there no longer had any kind of a lifting strap, so I had to lift it out by pressing my fingertips around the sides of it. It was awkward and also somewhat painful.
Fourth, lifting in the new battery was easy, but putting everything back together was every bit as much fun as it was t take it apart. See "Second" above.
It would have all been a lot easier if I weren't 65 and seriously overweight. I'm still fairly strong, but I am not nearly as flexible as I used to be and I don't fit into small spaces well.
I wasn't at all sure the car would start, even with a new battery, but it did start right up. Now I just have to do some basic cleaning and I can take it to CarMax to see what they'll give me for it.
I'm claiming victory, if only a small one.
If you did this you'd become a millionaire not a trillionaire because nobody would ever buy a new one.
Gotta build some planned obsolescence in there if you want a trilly