Where can I get a negative terminal clamp and ground cable for my 12v battery?

Wow... that 12v ground has lived a wild life!

Shocking!

You can get a replacement for these in the RV / 12v battery section of any major dept. store...

Auto parts stores sell them too, but the price is way higher.

 

For starters, the original mounting bolt to chassis is sheared off, so at some point it was loose and the person dealing with it likely got the threads crossed and then the bolt broke off. All the while the connection was so loose that it was throwing sparks every time it became connected and disconnected which is why you see all that burning around the old bolt.

Then at some point someone used a random screw to create a new ground to chassis, which finally solved the problem, but the main issue is that not only do you have an ancient 12v battery and in times of Covid with so much less driving it (needs to be kept charged) that is likely your problem but also whoever dealt with these problems managed to damage the cable a bit.

Let me know when you're ready to replace the 12v and myself and others will argue about your options for you. In the meantime buy a battery charger and replace that cable and also replace that screw with a more burly bolt. Though I suspect the condition of the cable is not the problem so that's a lower priority than charging or replacing 12v.

 

Ebay or junk yard part 82123-47020

Maybe somebody put in a non-agm battery without the oem terminal diameter or the lifespan of a deep cycle oem agm.

https://www.ebay.com/itm/04-09-TOYOTA-PRIUS-BATTERY-NEGATIVE-TERMINAL-CABLE-OEM-82123-47020/193874557690?epid=658173610&hash=item2d23d2fafa:g:020AAOSwt5ZgGC76

 

Water is not the issue, though in your part of the country rust definitely is the issue... As for replacing your 12v once you can't keep it going by constantly charging it when car is not in use I recommend this one: 12 Volt (12V) 55 Amp (55Ah) VRLA AGM Sealed Lead Acid Battery 55 AMPS HIGH CAP | eBay You'll also need to buy these bolts and two washers for each bolt that are slightly larger than both terminals to sandwich the terminals in between:

 

Wow looks like a crime scene back there.

 

Oh so that other new looking ground lead is the inverter. Don’t do that just affix the battery battery ground lead by itself should be bolted down using a bolt not a big self tapscrew that will not last. Should be able to tug on it hard when done and not move in the slightest.

Find another chassis ground spot for your inverter. Plent of bolts in the back hatch area.

 

I think he is suggesting you buy an agm that has different terminals than factory. You would have to buy bolts and washers and try to rig the existing cables on the different battery terminals.

On the terminal below it would be big washer, battery cable, washer and then bolt. My preference would be a Toyota battery for $100 more if you shop around at the dealers and ask for a discount.

 

Yes, but consider 1500 as peak watts and keep constant draw under 1100w.

And yes it fits in the same hole but it's slightly taller so you can do one of these to make it fit: 1) remove the bottom mount from the previous battery, 2) Put metal battery hold down bar in a vise and rebend it so it's slightly taller, or 3) Use a longer bolt to mount the hold down bar.

I've done #1, #2 often. Haven't done #3 yet, but soon.

As for pics, it just looks like any other battery and I can take a pic later but right now I have to go shovel snow so I still have access before next snow comes in 'because Prius no like the snow and our city only gets legit snow every 2-5 years. But if you want me to take a pic of how it looks I can do that if it helps people learn.

And grateful for you spending time doing research before you posted. That's much appreciated/speeds things up... You'll figure this one out... It's easier than most.

 

If you look at my picture there's a bolt right next to the original ground bolt. You can ground it there.
Sand down the chassis mating area under that bolt so the lug makes good clean metal chassis contact.
Grease up that mating connection and the bolt the lug and the terminal and bolt it up. See my picture. All the red stuff is synthetic bearing grease. Grease it up.

No corrosion back there. Ever.

Find another place to attach the inverter ground lead lots of bolts in the hatch to bolt it too. The battery ground lead is primary connection. Nothing but it and the chassis must be solid and conductive to chassis.

Before ever touching anything on that 12 volt battery remove the 2 black wires that are plugged into the top battery assy. One is thick the other is thin. They are plugged in on white plugs with locking tabs. Push the locking tab down with small screwdriver and gently pull out. When removed the 12 volt battery is disconnected form the car. Now you can maul that area all day and no sparks.

The thick black wire is the main B+ lead that goes to the front jump point under the hood. The thin black wire is 12 volt sensing for the inverter. Be extra careful back there with the 12 volt its easy to blow up the inverter by doing something stupid with the 12 volt rail we see many of those on this site.
Respect the 12 volt rail in this car. It does not like shenanigan's and you have exceeded the shenanigans limit.

 

That may be the twelve thousandth time I have heard "the guy told me" on this site. Who believes anything a guy is telling you trying to sell you a car? In fact anything a guy tells me I think ok I have to check that first.

Sand down the area where the battery ground tab will touch.

Don't bother measuring anything at the battery always measure at the front jump point to ground. That way you test the battery and its 8 different connections and the long cable it has to get through to get to the front fuse box all at the same time. It does not matter what the battery reads right at the battery it only matters what it reads when it gets to where its going to do some some work.

Measure the 12 at the front jump point Then turn on the headlights with the car OFF and measure it again. See how bad a voltage drop it has that will tell you the quality of the battery charge. It already incurs a .5 volt drop across the long cable and the 8 different connections in the hatch.

 

I explained the problem... And 12.7volts after the car was used only 3 hours earlier means battery is at the end of its life. Either get a charger for it, or get a new battery. Not sure why you think you can get by without doing either because obviously due to your car not starting, you can't.