Seemingly dead Prius turns on when touching negative battery terminal

Battery connections tight and body ground?

Posted via the PriusChat mobile app.

 

Sounds like a bad battery ground connection. Make sure the terminals are clean and check the negative cable where it attaches to the body. Charge the battery and have it tested.

 

It's best to trickle charge those 12 volts on a regular basis. Prius charging system is weak.

Posted via the PriusChat mobile app.

 

Disconnect the ground lead from the chassis. Sand down the area it connects to and the end of the ground cable. Apply synthetic grease to that area and bolt that lead back up the car chassis please see my pictures. The red stuff is 100% pure ester base stock synthetic grease. No corrosion ever there.

Then with ground lead still off on the battery side get some sandpaper and sand down the negative post of the battery till its nice and shiny then sand down the inside the neg lead ground post clamp. So everything is shiny and clean. Apply grease and bolt it back up.

By the way voltage sagging to 10.7 volts means your battery is really bad and will leave you soon. You may notice when you hit the READY button and the car is booting up and all the dash lights come on for a second you will also see a bright red triangle flash for a second. That's the only warning you get the battery is bad. Next stop is car won't start.

 

If you have a multi-meter. Set your meter to measure resistance. Hold your positive meter lead to the center of the (-) terminal post. Connect your negative meter lead to the car chassis (like the trunk latch, anything with bare metal). It should show 0 ohms. Now start touching and wiggling stuff to find out where the bad connection is located. If everything appears solid, it may be internal to the battery due to a bad mechanical connection between a bus bar and the terminal post. It happens.

 

how old is the battery? maybe an internal fault

 

Did you check the negative cable where it bolts to the BODY?

 

It seems as though everyone is pointing in the same direction on this thread, I hope he replies.
Some just disappear after their car is fixed never to return again.

 

The earlier symptoms clearly point to a bad / loose / broken connection somewhere, with a strong mechanical link to the jiggling or clamp compression of the negative terminal.

Keep a very open mind about where the actual problem could be. Besides visible connections, it could be a broken connector or wire hidden beneath insulation, or even a broken post inside the battery case.

Decades ago, when a dealership installed an AC kit to the first new car I ever bought, they disconnected a ground strap in the engine compartment. When putting it all back together, someone merely hand-threaded the bolt a couple turns then forgot to fully tighten it. I discovered some sort of problem a few weeks later when it failed to start late on a Saturday night in the next state. Jiggling things got it going, but I needed several more starting failures over the following week before finding the actual problem.

 

Sorry, missed your post, good luck.

 

It's possible for battery clamps and posts to feel totally mechanically tight and secure, and yet be oxidized enough even for stuff like this to happen.

 

Hey letting you know I have a bosch battery and when I newly installed it on a trip I had simular problems thing is now that you tightened the heck out of it it might happen to you. The terminals are lead based and over time you might lose contact again. I had to buy some small hose clamps and make some "ring shims " out of em, i.e. undo the clamp and brake off the screw part and wrap it around the terminal to make the clamp smaller or the post fatter, however you want to see it.
Just a hint for the future.
My $ .02
terramir

 

I don't know how they would work on a Prius battery but they make battery terminal shims.

Lynx Battery Terminal End and Adapter 07769

 

Over-tightening lead battery clamps tends to squeeze their ends together and, eventually, make it impossible for them to achieve the necessary pressure on the battery post.

Sometimes the overtightening is in an attempt to overcome bad contact because the battery post and clamp surfaces aren't clean enough. When they are clean enough to make good contact, the clamp doesn't need to be any tighter than the specified torque, and the connection won't give much trouble.

Or, the overtightening can be because the clamp is already squished from prior overtightening, and now can't do the job. In that case, I'd say replacement clamps are pretty easy to get and less fuss than cannibalizing a hose clamp for a shim.

 

Yeah well I was leaving from watching the eclipse about 1k miles from my home and this was the fastest cheapest way to fix the problem at the time 3 bucks for a set of hose clamps, a few loaner tools and about 20 minutes of my time. And the repair has lasted 1yr 6mo. And 12 days and still going strong ;- )
terramir

 

I'd say that getting to experience that eclipse in person was very well worth this price.

While that was my second totality experience, it was the first with weather good enough to actually see it. Wow!