2001 prius problem

i just picked up this car a while back and the main battery was dead.
I charged it up cell by cell to 1 bar and spins the starter a bit
then dies with error code P3120?

I also have noticed the fuel gauge is at 1 bar even after I filled it
with 5 gallons of gas.

The car has been sitting for a while. Apparently, the battery
was run dead before from leaving the lights on,
and they could never get it to restart. Of course, now its
probably been sitting for 2 years or so.

Not sure what the best route to go is. Is the transaxle toast,
thats what that code means apparently. although,
I hear some people have run with that error code for a while

At this point, I am thinking the main battery doesnt have
enough juice to start it or the transaxle is broken.
oh, my other thought is the transaxle has rusted up a
bit from sitting.

If both are bad, I might just resell the vehicle for parts
but if a new battery would fix it, that might make it worthwhile
to keep.

I was thinking of towing the vehicle in drive to
charge up the battery and/or just get the transaxle moving
a bit?

 

well, the main battery is holding at 270 volts or so, where
it was at like 5 volts when i got it. I realize that doesnt mean
its fully charged, but it is certainly better then it was.

i have also wired up in parallel a good 2005 main battery(to 28 cells of the
old battery) and a standard fairly new car battery for the 12 volt.

It will show 3/4 charge for the main battery for a bit then
it jumps back to one bar. I am charging the remaining 10 cells
of the old battery currently to get them a bit higher. how long
should it take to charge one 7.2volt cell to full charge with a
1 amp charger?

 

Hey, succes, I guess it worked now. The engine started and the car
drives now. Kinda of a jerky start but after a few trys its running fine.

Now getting error code p0115 and p3006.
The engine doesnt seem to turn off and so it runs off the
engine pretty much. I guess its a temp sensor issue.
I am going to leave it run for a while, maybe it will charge up
the batteries a bit.

also, its able to restart without the other batteries in parallel now.