200K Miles. Everything is great but it ran through a 2 year old 12v ??

If you're lucky, the battery issue may have been merely a loose connection at a battery terminal. Any chance a door wasn't fully closed? That can run down the battery within a couple of days.

Have you heard the engine "rattling noise" since last winter?

 

How many miles are on this vehicle and where is it driven the state?

 

Now you're over here in my area somewhere Virginia doesn't really get too cold there It doesn't really hear in central North Carolina either I would be monitoring that rattling and or bucking. This is the precursor to the dreaded head gasket failure and one of your plugs may be taking on some water vapor you might want to look now get it warmed up shut it off pull the plugs or at least pull the coils and see which one has all the rust and yuck in it maybe two then pull those plugs and have a look for water droplets on the two rusty coil holes The other two will probably be okay it's the one that'll be showing rust vapor red all over the coil top of the plug the whole well

 

Once a store gets the batteries, they don't charge them unless someone asked them too.
They will discharge on there own from just sitting. Best to do a 12 hour charge at 4 amps or less.
They you know it has a full charge. They inverter charges very slowly so unless you drive it for
8 or so hours they battery won't get a full charge.
Hopefully, this is the only problem you have with it.

 

Cold start rattle and 200k miles (presumably EGR never cleaned), you may have coolant getting past the head gasket, into a cylinder.

See first link in my signature for the EGR. It’s best done by 100k miles.

Is engine coolant level stable in the reservoir stable?

 

We run the crap out of ours too My girlfriend drives the three and it doesn't go through 12 volts generally not at all of course all of our lights and tail lights and everything on the car is LED even the interior bulbs and anything else we could possibly do to not be using much from the 12 volt we've tried to do but you know all the computers need it and our inverter seems to be charging it well so we let it go next we'll be using one of the UB batteries there's so much cheaper see what that does I've used them in other things with great luck

 

I’ve heard of reckless driving but that one takes the cake- Driving through a 12v battery

 

Almost guaranteed to be a head gasket on a 2010 with that many miles. While a spark plug "could" mimic that behavior it would be rattling longer than just for a few seconds on a cold start.

Two things are important to avoid being stranded with an engine failure:

1. Never run the car for more than two minutes if the temperature light comes on. You have an all aluminum engine that warps quickly when overheated. Verify the coolant level in the passenger side of the engine compartment.

2. Never run the car out of oil. Check the oil every fillup for a month or two to get an idea how much is being consumed. These engines are bad about oil consumption.

It would be a good idea to find an independent mechanic with Prius experience. They can save you 50% on major repairs versus the dealer.

 

It seems like you're asking about why the 12 volt battery might be bad and yet people are responding about your startup sounds. These are two different problems and if you're not a mechanic the diagnostic procedures are over your head. Who's the parasitic draw test.

But you also have to diagnose a startup knock and you haven't got a copy of text dream and you don't have the necessary tools to do the differential diagnosis. You're going to have to give this car to somebody with the experience to do the differential on the startup knock

 

She solved the battery problem with a new warranty replacement.

 

That's not solving the problem. If the battery went bad in two years you have to figure out why. Just replacing the battery doesn't fix the problem

 

If the battery was defective, the 12v battery problem is resolved.
If it was something else putting excess stress or draw on the battery, then it is not.

 

If the battery goes bad every 2 years we have to assume there's a parasitic draw until we can prove there is not. Just replacing the battery is a Band-Aid. Of course it's possible she was sold an old battery or some other possibility. But the diagnostics are required. You cannot just simply replace the battery without knowing why it went bad prematurely.