Going to buy a 2005 with a dead hybrid battery

Am I right in thinking there's 2 seperate coolant systems? I'm going to have to replace the water valve since I have an error code for that.

 

I did pay $500, but there's a reason it was only $500.
Obviously the hybrid battery is on it's last legs, the clear coat on the roof and spoiler have failed,a few other error codes, there's a decent dent in the right rear quarter panel and a ding in the left front quarter, the hatch handle piece will fall out if you try and open the hatch with it. The interior also looks pretty grubby, but that seems to be a way a lot of the beige interiors look even at higher prices.
I had arranged to buy one for $1200 a few weeks ago, made an appointment at the sellers convenience and then the bugger sold it out from under me, but that one was in great shape with only the battery issue (as far as I could tell from communication and pictures).

 

Supposedly it's had its battery replaced before. What with? I've no idea, but I'd say some form of reconditioned battery.

 

I did a VIN lookup on it to find the spec. I didn't see a service record search. That could be handy, do you have a link by any chance?

 

So I got that Toyota service history, all looked pretty good and fairly regular until the last entry in Feb of 2016. It looks like they've been tackling mis-fire issues a intermittently since 125,000 miles.

It got a new short block at about 80,000 due to coolant consumption.
There's a considerable number of cleaning the intake and throttle body services.

Feb. 2016
CHECK ENGINE LIGHT ON,REPORT ~|~CHECK ENGINE LIGHT ON,REPORT ~|~ ~|~189157 100 CHECK CODES HAD CODE P0300 P0301 P0303 AND P0420 MISFIRE CODES ONE CYLINDER ONE AND CYLINDER 3 TRIED SWITCHING COILS AND SPARK PLUGS STILL MISFIRING ON 1 AND 3 CHECK COMP WAS LOW ON CYLINDERS, CHECK WITH BORE SCOPE HAS A LOT OF CARBON BILLED UP

How does one get rid of that carbon buildup? I read a thread where someone had the same issue and ran I think 5 bottles of Chevron Techron through their tank in 5 consecutive tanks of gas. He was well happy with the results.

Thoughts?

 

Is this where a good old fashioned Italian tune up comes into play?

 

For me to buy another Prius or a VW TDI we'd be spending about $5000-7000 for a decent one. I'm going to see what we can do with this. I'm a full time student and it'd be nice to just use this for a few years, upgrade the campervan and stash a few grand for a rainy day.

I've been looking up techniques for getting rid of the carbon and so far found sucking in water or seafoam into a vacuum line, has got some peoples cars running better. Can you use the vacuum line connected to the PCV as that would go into all cylinders?
I've heard a mention of a soak but not a description of the process, so not sure how that works? Maybe pull plugs and spray something in and let it soak? Then drive like a bat out of hell?
I also read about doing a half tank of E85 mixed with regular.....research continues.