Battery dead but when tested it shows up as Good

if your dash didn't light up, it might be just a bad combination meter. This is a common failure on older Prius cars. You can tell if your car starts by pressing the start button and waiting about 10 seconds for the engine to kick on.

 

You are having issues with your 12vdc battery. I see no reason to bring your drive battery into the conversation.

It could have been due to a loose terminal connection on your 12vdc battery.

Mine has been drained empty one time when the rear hatch lid did not shut completely.

 

You're 12 volt battery can easily show 12 volts It just doesn't have anything behind the 12 volts If you were to short the battery terminals for say 10 seconds it would not recover the 12 volts immediately like a good battery would That's how you used to test the battery The LISLE battery tester was a silver box with these heavy cables without any covering on them and a button and you push the button and held it until the meter moved until the cold cranking amps were revealed on the scale and then you let the button go and if you were looking in the grill of this device you'd see those tungsten bars or whatever they are they turn almost red hot basically shorting the battery for 10 15 18 seconds depending on the CCA and then when you let go of that button it's supposed to recover the 12 volts immediately If it doesn't well it's no count.

 

did auto zone give you a print out? how old is the 12 volt?

 

Why do u think that is? What testing have you done?

 

Our mechanic uses one of those to test a battery's Load capacity. It is much more accurate than a simple voltage measurement and gives you an idea of how many amperes the battery can provide.

If you have reason to truly suspect your 12vdc battery, get it tested to learn its Load capacity.

I find it kind of disheartening when I read so many people who at the first hint of a 12vdc battery problem want to jump on the drive battery. When there is no indication of an issue there.

 

He took it to auto zone, pretty sure they do a load test

 

Get your own load tester? My pref would be Solar BA9 (have an older version). Autel and TOPDON are popular.

 

They do and it's with some algorithm on a computer that runs off 5 volts or something so there's always that a real test of a battery is to take two pieces of metal and short the battery A coat hanger works well It should light up that coat hanger red hot and it'll usually bust in the middle where it was bent before and when it does that and you put your test leads on it and it says 8 volts it's about that battery is no count If you put your test leads on it and it says 12.7 that battery is the shiznit. That's how you load test the battery or how it was done for 50 years and then everything turned into solid state electronics and computers and algorithms and as we see algorithm sometimes be not the thing.