I guess I haven’t been driving it enough (car won’t start)

Idk if it's been said before, but turning on the climate control actually charges the battery. I tested it with a voltage meter. 11v off and 13v with climate on

 

That's really good to know. Were you in a particular operating mode, i.e. EV, HV, Sport, for your measurements?

In my 12v battery measurements so far, I believe I've had Climate Control ON in all cases, but I'll take care to assure that is the case every time in the future. I usually have it on whenever I drive the car. I'll also confirm your Voltmeter test with the Battery Tracker, to see if it reports the same variations when switching CC on and off.

 

I mean CC as in the remote climate feature in the Honda link app or the climate button on the key fob. My car was turned off when I tested the voltage.

 

Aha, that make sense. It reasonably would do that with the car not fully running. I misunderstood your first post, and assumed that you meant CC on or off while the car is on. FWIW, prior to seeing your last post, I did some testing while running the car, in each mode, and CC on or off made no difference at all to the applied battery voltage, so that isn't a factor to my HV mode charging issue.

 

Yesterday, I looked at this...

Outbound, I was in EV mode, and the voltage was always 14.4. I switched to HV for the 2nd half of the trip, and the voltage was always 12.4.
Home-bound, I started out in HV mode, and the battery voltage was always 14.4. I switched to EV half-way home, and the voltage was always 14.4.

The Outbound leg was during the day, and the Home-bound leg was at night (headlights on).

I believe the moral is that the Clarity charges the 12V battery when it needs to be charged. This is indicated by the 14.4V level. In my case, during the day in HV mode it did not need to be charged so it was 12.4V. At night (with the headlights) in HV mode it needed to be charged, so it was 14.4.

My guess is that you will likely experience both charging and non-charging conditions in BOTH EV and HV modes. Although during my experiment, I never saw non-charging in EV mode, I believe it will occur sometimes.

 

From your observations, it appears that the Clarity does not have a sophisticated charging algorithm for the 12V battery.

14.4V seems a bit high for a continuous charge, especially for a battery that doesn’t take the hit of actually starting an engine every time we take the car on a drive. I’d expect to see voltages in the 13.9-14.1V range upon “start up”.

The 12.4V reading is indicative of a fully charged battery at a resting voltage of 12.7V, that has a small load being applied. I would suggest that there is no charging occurring when a reading of 12.4V is observed. A float, or maintenance, charging voltage of 13.1-13.4V would be typical.

It is peculiar that the voltage just sits at 12.4V or 14.4V while driving. Almost as though it is either on or off until a voltage signal calls for a change. Hell, an alternator is more sophisticated.

 

This does not alter the basic picture of on/off with the charging algorithm, but I just wanted to mention that my measurement technique is the text display that Honda Hack places on the infotainment screen. I have no idea specifically where this voltage is being sensed, or with what precision.

 

I just took some voltage readings from the battery, while parked. It seemed safer that way. After a full charge, overnight, prior to powering on, the battery voltage was 12.62V. I closed the drivers door and waited for the interior lights to go off before checking the voltage. I then proceeded to turn on the DRL’s, headlights, both low and high, and left the door open so the interior lights were on as well. Checking the voltage after adding each load, it dropped to 12.30V.

I then powered up and the voltage read 14.59V. I turned on the headlights, radio, fan, A/C, seat heaters, rear defroster, and front defroster. With each new load, voltage ticked up, reaching a maximum of 14.82V.

After all these antics, I plugged in the charging cable. The HV battery was drained enough to initiate charging. Voltage while charging was 13.36V. Perhaps the charging algorithm is sophisticated after all?

 

We would expect nothing less from a cutting edge vehicle, but... As usual the details of this algorithm elude us !

 

As you may have guessed, I’m not that much into the nitty gritty. My experiment this morning satisfies my curiosity about the 12V charging system. I’m convinced that it doesn’t sit at 12.4V or 14.4V and that the charging protocol may even be appropriate for a 12V battery.

 

Thanks MrFixit for taking the time and effort to test your Clarity and respond with your results. I want to reach the same conclusion, that the Clarity is making a decision whether the battery needs charging or not, whether HV or EV mode, and applies either the high level charging in the 14.5v range, or the low level (no charge?) 12.6v battery level.

So far, though, I haven't been able to replicate the decision behavior that your reported on my own Clarity. I've made a bunch of drives the last few weeks, in EV mode with battery level prior to startup as high as 12.53v, and the car has invariably held the battery level at the higher 14.5-6v level throughout the drives. In contrast, I've done a number of tests in HV mode with initial battery levels as low as 12.34v, but it has always provided a sustained lower battery voltage of around 12.6v level. So far, it has never applied the higher voltage for more than a couple of minutes, if at all, and always stays at that low level for the rest of the drive.

Either the Clarity has a different standard of when it "needs charging" for EV and for HV modes, there is another variable involved, or perhaps I have a defect in my vehicle. I think my next move is to let the battery voltage to decline, without charges, as much as I can, to see if I can ever get it low enough to trigger the HV higher charge voltage to be applied.

I wouldn't really care about the HV charging concern, since I use it so infrequently, except that it could leave the car more vulnerable to discharge when we drive 70 miles to the airport, in HV mode, with no real charging to the car during the drive, leave the car for multiple days, and find a dead 12v battery on our return. Granted, I can use our quick battery jumper to kick it on, but that shouldn't be necessary, and those discharges are not helpful to the life of the battery.

 

I purchased my 2018 clarity Dec 30, 2017. The 12 volt battery lasted 3 years 1 month before I had to replace it (no longer under warranty) because of a bad cell. I also wonder if the 12 volt battery is being charged properly. My voltage reading when the car is on is about 14.5-6 volts which I also think is too high.

 

It's kind of funny...

I believe @vicw is worried about undercharging, and @bpratt is worried about overcharging !

 

That is ironic, @MrFixit, but oddly and possibly both valid. Probably the happiest folks are working at Honda Engineering. I just wish we were privy to the 12v battery charging maintenance details and and charging scheme.

 

My battery was 3 days short of the end of the 3 year warranty period, when it failed to start, but the dealer blessed the battery as still good. I do suspect that the Covid-19 avoidance driving pattern may well have contributed to, or perhaps caused the voltage depletion problem, and the battery still might have had a year or so of use left, but to avoid the risk of having my wife stuck with it failing again, I replaced it myself.

 

Well, if there is an issue with the 12V charging scheme, maybe it will be recognized and fixed at some point (although we have seen NO interest from Honda in fixing ANYTHING). There is plenty of room for software enhancements and fixes, but there just haven't been any.

If it's any consolation, although a battery should last more then 3 years, there are worst things in life than having to buy a new 12V battery every 3 years. This is certainly a notch down on the worry list than unexpected degradation / failure of the HV battery system in my opinion.

 

I completely agree. I've always expected battery life between 3 & 4 years. The only unfunny event is getting stuck somewhere with a bad, or depleted one, and no help in sight. I now have one of the little jumper batteries at the ready, and I've bought each of our kids one, too.

I only mentioned the failure vs. imminent warranty expiration for its irony. The battery on my prior Honda also failed just shy of the expiration, but the dealer popped a new one in, no questions asked, under the warranty.

 

I’ve read that a Honda replacement battery carries a 100 month warranty. The first 36 months provides free replacement. After that it is prorated. There may be some value in getting a Honda battery rather than something from Sam’s/Costco, if the latter only offers a 36 month warranty.

Interestingly, in my previous vehicle I had installed a battery with an 84 month warranty. Unheard of these days. It failed at 83 months.

 

Yes, it does come with a 100 month warranty, as you described. I thought of Honda last when I was looking to buy the replacement, assuming their price would be higher than the competition. It's amazing how much higher battery costs are today. I was shocked to see some parts shops quoting $160-170. The Honda dealer sold it for about $140, which seemed competitive. The parts guy brought the battery out to my car, and placed it in my trunk. They did the same when I returned the core. There wasn't any core charge, but they took it back.

 

So I was going to post how those claiming different charging voltages were crazy, that the DC-DC converter should just put out single voltage, and any discrepancies had to be either in your head, from reading a screen wrong, or something. But before I did, I thought I’d test it myself, with a pretty accurate multimeter and an old lighter cord I had cut apart for something else and an experimental drive. Well, sure enough, you’re right! Here’s what I observed, in my 2020 Base:

• When starting and driving EV-only, the voltage remained at 14.7V the entire time, including a 15+ minute EV drive.

• As soon as I got the engine to run (either using the HV button or just kicking the accelerator past the detent), a few seconds later the voltage went to 12.69V and stayed there until I shut down the car, even when the engine was off and back in full EV mode. No matter how long I drove in EV (another 10+ minutes) it stayed at the lower voltage.
  
  
• When I plugged in the charger (L1 but shouldn’t matter), I measured 13.45V at the battery; that should be enough to charge the battery.

• When off/not charging, I measured 12.2V at the battery, so at least when running at 12.69V that means power is indeed coming from the DC-DC converter and not draining the battery, but it may not be effectively charging it either.

I wonder if people who’ve had more dead battery problems tend to have the engine run early in their drive, thus never really getting a good charge while driving. And when they take it to be tested, the car starts in EV and the charging system puts out 14.7V, so it *looks* fine.

It’s weird, because the engine running should have nothing to do with this -- there’s no 12V alternator or starter since the engine starts and generates electricity right to/from the HV system, and that wouldn’t explain why it stays low after the engine shuts off. I can’t imagine why they would have designed it this way intentionally, but there may be a reason. Pure ICE cars draw significantly from the battery every time they start, so there’s more need to replenish while driving than our cars.

I doubt there’s any real intelligence here -- once the DC-DC converter voltage is there the car can’t tell the 12V battery’s state; so I don’t think it’s actively deciding to charge or not charge. I’d bet the above behavior is true regardless, but I was wrong with my initial thought so who knows.

No idea how we’d get Honda to explain, acknowledge, or fix this (if it’s indeed broken).