12v fully charged back but can't start car

I would try the 'reboot' you mentioned. Do you have someone who can watch the volt meter while you press the 'start' button? Maybe you have a failed cell or something and your voltage is sagging too low if there is any load (like the computer or high voltage contactor) applied. Alternatively, you could try leaving your charger hooked up while you try to start. Given the low power draw of our cars, I wouldn't expect it to cause an issue (and most chargers have overcurrent built in anyway.)

As far as your pedal not going down, if you pressed it a couple times already, you probably bled all the vac out out of the brake booster. It should go back to normal as soon as the car gets powered up. (At least I assume we still have a traditional brake booster - just driven from an electric pump. Perhaps I am wrong.)

 

Strange. I know one time when I killed the 12-volt battery on mine I didn't need to do anything special once it was recharged.
(Edit, realizing now that was my former Fit EV)

 

My experience with a dead 12V battery was that the key was required to open the door and absolutely nothing came on inside the car after pressing the power button. No dash display, no interior lights, nothing.

After connecting a lithium jump pack, the car came to life and the display informed me of all the terrible things that could occur should I fail to deal with them before proceeding. I drove it 20 miles and then used a conventional charger on it overnight. That was 10 weeks ago and it has been trouble free since.

I’d say that you don’t have an issue with the 12V battery. Your display came on and when you connected the gooloo you essentially replaced the 12V battery.

It may be time to utilize the Honda Roadside Assistance program.

 

I haven’t used roadside assistance.

They may be able to diagnose and fix the problem on site.

With the Covid situation, you probably won’t be able to ride in the tow truck.

I’d guess that if towing/flatbed was necessary, they would tow to the nearest dealer.

 

Well, unfortunately with a highly technical vehicle like this, it has been demonstrated that there is a drain on the battery when the vehicle is off / not used for an extended period.

I do not have an explanation as to why you are having trouble recovering, but I think it is important to emphasize that we should all be aware that your battery WILL drain down over time.

Bad things happen when 12V lead acid batteries go stone dead... I would not expect the vehicle to go 'bad' as you have unfortunately experienced, but it is very hard on a battery.

I suggest that if all possible, do not let the car sit completely idle for an extended period without intentionally driving it for a bit, or connecting a battery tender / minder. My instinct is that an "extended period" would be several weeks, maybe a month. Shorter than that is probably OK.

Please keep us posted as you resolve this problem !

 

I'd suggest leaving the 12-Volt battery disconnected for a half-hour. What can you lose?

 

In general, I agree with MrFixit.

My personal experience differs somewhat. In ~15 months of Clarity ownership, the car has sat idle, unused and unplugged for a period of one month and another of 6 months. After the one month period the 12V battery read 12.45V and the car powered up without issue. After the 6 month rest, the 12V battery read less than 2 (two) volts. I measured it at least a half a dozen times.

We have some high quality meters to measure voltage. I measured voltage on the other car, 12.7V. A AA battery, 1.8V. A lithium 2032, 3.2V. The meter reads accurately. With the lithium jump pack connected, it measured over 12V. Once the car powered up and the DC/DC converter was operating it measured over 14V.

The car has started every time for the past 10 weeks and 2500 miles of daily driving. I can’t explain it. Recently I had to replace a 12V battery in a portable generator after attempting to bring it back to life for a week. It never got above 7V.

I won’t be due for an oil change and tire rotation until March. I’ll have the 12V checked at that time.

For Luke001, I don’t believe you have a 12V battery problem or that you will have any issues dealing with Honda on a warranty claim to resolve the matter.

 

If this is really true, I believe it is the first example of a traction battery failure that has been reported in this forum.

There was another owner who was asked by Honda to exchange his battery for a new one (it had not failed, but something prompted Honda to ask to get it back).

If they are willing to communicate any details to you about the nature of the failure, please try to gather whatever information you can and report back. There are a lot of technical people here who would like to learn more about a traction battery failure.

 

This vehicle does not have an alternator.
The 12V battery is charged from the traction battery.

Are you certain that the problem is not with the 12V battery? There is a world of difference between a 12V battery failure and a failure of a traction battery. Did they specifically tell you that the repair would have been $8500? If so, that sounds like the traction battery. On the other hand, I would expect it to take longer than 5-8 business days to obtain.