Dead 12 volt battery experience

I believe HV Charge mode has nothing to do with charging the 12V battery. It only uses the engine to charge the HV traction battery. The HV battery charges the 12V battery, but it takes time while the car is running in EV or HV mode.


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If the car is ON/READY, the 12V battery will be charged by the Lithium battery via the DC/DC converter/charger. You don’t even need to drive around.

A flooded battery isn’t going to take a charge after 2 miles of driving.

 

I leased a full battery electric Clarity for a couple of years and twice I was stranded with a dead 12 volt battery. I have no idea why. Since then I always carry a portable jump starter in my trunk. They only cost about $50 on Amazon and they work really well.

 

The lithium jump packs weigh about 2lbs.

 

Using Accessory mode will really deplete the battery. For idle use of the radio while parked turn the car on, in EV mode. That will apply about 14.55 V continuously to your 12 V battery, and increase its charge, in fact, I've occasionally used that mode, leaving the car running in EV mode, but inactive, for about an hour to provide a lazy battery charge.

There is also an anomaly on the Clarity, at least on mine, when driving in HV mode during daylight conditions - if the headlights are set to Auto, but not actually on, it will initially provide the 14.55 V charge, but will drop back in around 90 seconds to a 12.6 V charge rate for the rest of the driving session. If the headlights are set to ON mode while driving during daylight, the full 14.55 V charge will be applied. I've been monitoring the battery levels on mine, using a continuous monitor, and I've seen that pattern consistently.

 

That’s interesting. I’ve only taken some readings at the battery with the car at rest in EV while turning various accessories on and off.

12.6V is not what I would consider a charging voltage as it is below the resting voltage for a 12V battery. Have you noticed if the voltage changes when you turn on any accessories such as the fan or stereo?

 

Online, or, for immediate gratification, an auto parts store, Battery Systems, Batteries + Bulbs, Costco, Walmart, etc.

 

The product description will typically indicate what size engine the jump pack is capable of starting. We don’t need the jump pack to start the engine. It only needs to provide enough power to activate a switch. So, one of the smaller, less powerful models might do the job. However, if you have another vehicle or need to assist a damsel in distress who can’t start her 5.0l Mustang convertible, you may want to consider a larger model.

 

I really haven't tried turning fan or stereo on and off, but the headlight correlation is so consistent that I now always just turn the headlights ON during long daytime HV driving sessions. I don't think the Clarity is making any fine adjustment according to the current state of charge on the 12 V battery, or demand. It seems to be a very simple correlation with the headlight status.

The following screenshot shows the 12 V battery voltage for one 24 hour period. The midnight to 1AM period reflects my Siemens car charger being active, with 13.3 V applied to the 12 V battery.

My afternoon drive started about 2 PM and was a long session in HV mode, with the Headlights set to ON, resulting in an applied voltage of 14.58 V. At about 3 PM, while still on that same drive, I switched the headlights back to AUTO, and the applied voltage dropped back to 12.57 V for the remainder of the last 10 minutes, or so of that drive. On my return drive, starting shortly before 4 PM, I put the headlights again back to ON, resulting in the 14.58 V applied, and I switched it back to AUTO around 4:20 PM, with the resulting 12.62 V, until I returned home around 5 PM. The two short evening drives were both in EV mode, with an applied 14.57 V. That higher voltage level is always applied in EV mode.

(The higher than usual voltage decline after the last drive of the day is likely attributable to the video cam that I recently added to the car, with a 3 hour timeout. The behavior of the various charge levels vs. sources has been present since I've been monitoring the battery back in February, long before I installed the cam.)

 

I would like offer a theory...

The Clarity has some kind of algorithm that determines when it is necessary to enter the "charge" mode (14.x volts). One part of that algorithm undoubtedly involves the current load condition. When you force the headlights on, there is apparently a sufficient load to invoke the "charge" mode. Suppose you never turned on the headlights at all (only daytime driving, and headlights in OFF position). Would the car never charge under this condition? - I think not... It's just that another part of the algorithm will trigger charging at some point later when it is needed.

I contend that the vehicle is smart enough to charge the 12V battery on an as-needed basis. Yes, you can force it to charge by turning the lights on if you want, but I believe all you are doing is wasting energy which could otherwise be used to propel the vehicle.

You have an excellent setup with your battery monitor to prove this theory. In your travels, try to minimize 12V battery use. Don't ever turn on the headlights (just to force charging). I think you will definitely see charging cycles that occur without any specific actions on your part.

It is interesting that while charging the HV battery, that the 12V battery is being charged (albeit at a lower voltage, 13.3). It is quite possible that "charge" mode may never need to be activated (in-between HV charge cycles) if 12V demand is very low. You could be deceived into thinking the 12V battery is never being charged, but in reality it is (every time you charge the HV battery). That could be perfect adequate when there is a low demand while driving.

 

Your theory could be correct, and I am happy to try to prove, or disprove it, but in reality, I don't drive in HV mode frequently enough to perform the experiment in a timely manner. I usually go for extended periods using EV mode only, with brief runs on HV mode about once a month, or so, just to keep the engine from drying out. In every one of those short HV runs in daylight, and one that I did for about 150 miles, starting with a low battery voltage level, with the headlights set to AUTO, that I've monitored so far, the charge level dropped back to 12.6 V within a minute, or two. I'll post an update back on this thread if I ever see an exception.

EV mode always applies the 14.6 V charge to the battery - every time, for as long as the drive goes on, and I have a hard time rationalizing how or why the Clarity would apply a sophisticated algorithm to decide if the higher level charging is needed or not, in HV mode, but wouldn't do the same thing in EV mode. Also, I really doubt that forcing the higher voltage to the battery in HV mode to trickle charge the battery is using any significant power.

 

I agree with this. Yes, a little bit of trickle to the battery, plus you are powering the headlights which probably amount to ~ 50 Watts.
It is indeed curious why it seems to behave differently in HV vs. EV. You could run a 50 watt load for days without depleting the HV battery.