New 12V battery: car won't start

My 2006 Prius does not start, even after I just put a brand new 12V battery in. A few weeks ago the car had been on the parking lot behind my apartment building for a while and I had not used it for several weeks. I could not open the door with the fob so I did it manually and checked the 12V battery, it was at only 2.9V (under load) so shockingly low. So I charged the battery overnight hoping I could still revive it but my expectations were pretty low. To my surprise it started the next morning.

But a few days later it did not start anymore and I decided I needed a new battery, the old one had probably been drained way too low and was about 6 years old. I ordered a new one, it arrived yesterday and I just installed it. It reads 12.8V but the car still won’t start, I can hear the brake booster humming when I press the pedal and the headlights burn bright, dome lights work fine but it won’t start and nothing else on the dashboard comes on. Only the open-door symbol does light up when I open a door but that seems to be all.
Just to make sure I checked the old battery, it was at 11.7V so maybe there was not even a need to replace it. I do not drive regularly and mostly short distances but I had the hybrid battery replaced last year and it would be nice if I could use the car for a few more years.

Any suggestions on what to check next? I already had a look at the IGN fuses and they seem to be okay. I tried the spare key fob but that did not make a defference. I heard something about the fusible link giving problems, just by looking at it it seems ok but I don’t know how to check if it is still okay. Hope someone can help.

 

Thanks for your response. New battery is at 12.8V and if I turn all the lights on, doors open, honk the horn it drops to 12.3V. Safe to say the new battery is excellent and has more than enough power. Car simply does not go in Ready mode.

 

About the same as directly on the battery bisco. I have a feeling the receiver of the keyfob somehow does not work. Without pressing the break pedal the startbutton should light up green when pushed but that does not happen. Tried the spare keyfob but makes no difference. Could not find any blown fuses under the hood. Will check the ones under the steering wheel this afternoon. To make sure I will also disconnect and clean the terminals on the 12V battery once more.

 

Thanks Jerry, it could be something simple like that. I have made stupid mistakes like that before. There is a big connector on the + and also a small single wire connector. That should be all, right? I have the European version but I guess it is the same for a US Prius.

P.S. When I changed the battery before years ago I only took the 2 clamps off. This time I removed both connectors first, left the one on the control box on and simple moved it to the side. Put the new battery in and reconnected both connectors.Then screwed everything back in place.

 

I tried that Jerry. I have a ScanGauge 2 which I have used a lot in the past but when I plug it in it cannot connect with the car 'connection failed'. The device clearly detects the +12V, powers up and tries to connect but simply does not 'see' the car. Also, the car will not go in Ready or even IGN ON Mode, maybe it has to before it can connect to it. So that could be the reason for failing to connect.

What is most puzzling to me is how a new car battery could damage anything in the car without blowing a single fuse. I found another thread on this forum where, after putting a new 12V battery in, the dash would light up but not start because somehow the brake fuse had blown. Could take a while to figure that out but at least that makes sense.

This does not make any sense at all: a car does not stop working when a new 12V battery is placed. I replaced the battery before some 6 years ago, it is one of the simplest things you can do yourself. Very frustrating. I guess I could have it towed to the dealer but they usually charge you an arm and a leg, no way to check if what they claim is true, not sure if a 2006 Prius is worth it.

 

Yes it does bisco. When I insert the fob and press the start button nothing happens. The led on the Start button should light up green when I press it but it does not. No ACC, no IGN ON, no READY.
With the head light high-beams on (they still work) the voltage drops from 12.8 to 12.3V so under load the voltage drops a bit but not by much. To me the new battery seems to be working fine. Except for the door-open indicator nothing else on the dashboard lights up.

 

Yes, all fuses under the hood and below the steering wheel are fine. Borrowed a realy (contactor) tester from a friend and will test those tomorrow. I more and more have the feeling that the problem occuring during the battery swap was purely coincidental. Could be the Start button or fob receiver. Anyone have schematics of the wiring in that area?

 

Not sure about rodents but I have had issues with moist in the past: even had windows frozen on the inside during winter and the radio did not work for a few months, then suddenly started working again. Could be a buildup of corrosion causing bad contact somewhere.