No voltage measured across "12V" battery after recharging

Hello folks,

Last weekend, I tried to use my Prius after it sat idle for a month and a half. However, I found that the car was utterly unresponsive: the door locks wouldn't work, the ignition button did nothing, no dash lights, and so on. I thought that the "12V" battery might be dead as a result of the prolonged period of inactivity. I tried to measure the voltage across this battery with my voltmeter. It reported no voltage.

So, I tried to charge my battery with a "DieHard 71219 6/12V Shelf Smart Battery Charger". The charger showed that it was charging for about 2 hours, then declared the battery to be fully charged. However, still the car is unresponsive. Furthermore, when I try to measure the voltage across the terminals of the battery, I am again seeing 0 V.

The battery is pretty new. I bought just late last year. Furthermore, I bought it from a local Toyota dealer, so it's not like it's some sketchy off-brand.

Anyone have any analysis of the situation? Do I just have a bad battery? Are there any other tests you recommend before coming to this conclusion?

Feel free to ask follow-up questions. I'm happy to provide additional details that might help you diagnose the problem.

Garrett

 

Thanks for weighing in, guys!

Fortunately, my wife has a Prius with a working "12V" battery, which allows me to take comparative measurements. If I try to measure the voltage of her "12V" battery with the same voltmeter, it reads 12.4 V, and also reports "DC". So I don't think my voltmeter is the problem.

 

Any other suggestions for what I should check before I take the battery back to the Toyota dealer?

 

That's a good question. I wondered the same thing. However, when I try to measure the voltage across the battery terminals during or right after charging, I'm not seeing any voltage. Only after making this observation did I notice that my voltmeter says "DISPLAY ON > 10 V", which I take to mean that it won't report anything less than 10 V. If that's true, then all I can say with confidence is that the voltage is less than 10 V.

 

I'm realizing that this means that some of my prior messages were unfortunately misleading. Anywhere where I've said I measured "0 V" or "no voltage", this should be reinterpreted as "no more than 10 V".

 

Another update that might be important... Yesterday, even though I had already tried to charge the battery once, and the charger told me that it was "charged" after 2 hours, I decided to try to charge it once again. So I hooked up the charger again, and the thing sat in the "charging" state for something like 8 hours(!) before it finally said "charged".

Furthermore, when I then tried to start the car, I could see *some* signs of life which were all previously absent. In particular,

1. There was a little dash light indicating that a door was open.
2. The two little green lights on either side of the key fob slot were glowing.
3. There was an orange light on the ignition button.
4. When I pressed the brake pedal, I could hear a clicking sound.
5. I could turn on the dome light, but it was very faint.

However, I still could not start the car. Pressing the ignition button had no apparent effect.

This morning, I confirmed that I could still turn on the dome light. It was still very dim. This suggests to me that the battery successfully held at least some charge overnight.

I once again hooked up the charger. Despite the fact that it had declared the battery to be fully charged last night (for the second time), this morning, it again said that it was "charging".

I'll add that the battery charger manual says that it could take up to 10 hours to charge a "50% discharged battery".

So, everything taken together, the hypothesis that's developing in my mind is that the battery charger is, indeed, charging the battery, but that it just keeps prematurely declaring the job to be done. I'm planning to leave it charging today as long as I can to see if I can get more signs of life from the car as a result.

Any alternative interpretations of the facts?

 

I'm pressing the leads of my voltmeter directly on the battery posts. I used the same method to successfully measure the voltage on my wife's Prius battery.

 

I will also add that my car insurance is through Metromile (now Lemonade), which means that I have one of those sensors stuck in my OBD2 port that reports my driving distance to Metromile. I'm pretty sure that this thing continues to draw power from the 12 V battery even when the vehicle is off. If so, that would be the "parasitic draw" you've inferred.