Idea for 12v battery longevity if your Clarity isn't driven frequently

[KyleH]

Hello owners - I ran across something I felt worth sharing with the community. Apologies if this is common knowledge, but after poking around a bit, it looks like battery life is short on these 12 volts. My wife has an '18 Clarity. It went off warranty during the late Spring this year. Like many, with Covid, we work from home and don't drive it often. I think we have a tad over 20k miles on the car. I recently picked up a nice trickle / maintainer charger for my 2 other cars I rarely drive and thought I'd pop the hood on the Clarity and get a look at it's battery while I was in the mood. To my surprise, the little eye was red, indicating a low charge. She probably drives the car 1 or 2x per week and the vast majority of the trips are less than 20 minutes each way.

What I deduced was that the amount of driving she is doing just isn't enough to charge the battery. Given we rarely drive the car, we therefore don't have it plugged in very often either. I try to keep the EV battery balanced in the 40%-60% range and then disconnect the charger. I went ahead and stuck my trickle charger on the 12v for a couple days and got the battery back to healthy - good voltage and the blue ring in the window came back.

This got me curious - and this is what I wanted to share - on the 110v charger (I'm assuming 220v same), when the car is charging, I confirmed it is also charging the 12v battery. As a result of this insight, I decided what I would do is leverage this feature. So now I have a routine set on my smart outlet to kick on for 30 minutes every night to act as a charge / refresh for the 12v battery. Over the course of the week with a drive once or twice a week, it's not enough to overcharge the primary EV battery, but saves me from having to drag cables over to and keep the hood popped to preserve the 12v - something the wife would not be please with when she needs to use her car.

Anyway, just wanted to share this. BTW, I did test to see if the charge on the 12v battery is in effect when I deactivate the EV charger from the car - but unfortunately it isn't. When the car's EV battery has it's charger shut off, this shuts the charge off of the 12v as well. This would be a pretty nice feature though to keep that little 12v in tip top shape... calling Honda engineers.

 

[MrFixit]

So now I have a routine set on my smart outlet to kick on for 30 minutes every night to act as a charge / refresh for the 110 battery

Sounds like a good idea.

Just a word of caution - make sure your smart outlet is up to the task,
Some are only rated for 10 amps.
You must have at least a 15 amp rating.
Also, I'm sure the quality of these can vary greatly. This introduces another set of contacts (unless the smart outlet is hard-wired into the wall). If you have a weak connection this can result in high resistance and overheating at the plug.

 

[KyleH]

Sounds like a good idea.

Just a word of caution - make sure your smart outlet is up to the task,
Some are only rated for 10 amps.
You must have at least a 15 amp rating.
Also, I'm sure the quality of these can vary greatly. This introduces another set of contacts (unless the smart outlet is hard-wired into the wall). If you have a weak connection this can result in high resistance and overheating at the plug.

Yep. Good call. That's very true. There are lower rated units. But I use higher amp-rated for the heavier draws and have had really great results over the years for the relatively low cost of entry.

 

[BrianRC]

Why not just use the car's built in timer or the HondaLink app to charge the car for 30 minutes every evening?

 

[KyleH]

If I didn't have the wifi outlets I would probably do that. Sadly, my generic application that controls my wifi enabled outlets are more reliable and user friendly than the Honda app.

 

[BrianRC]

I agree the app can be a pain, but you can also set the timer with the steering wheel controls.

 

[Landshark]

To my surprise, the little eye was red, indicating a low charge.

Did you measure the voltage during the red eye event? That window is frequently misread. If the car powers up, the battery is good.

So now I have a routine set on my smart outlet to kick on for 30 minutes every night to act as a charge / refresh for the 12v battery. Over the course of the week with a drive once or twice a week, it's not enough to overcharge the primary EV battery, but saves me from having to drag cables over to and keep the hood popped to preserve the 12v

In my opinion, this is way too much work. A couple of brief drives a week should be sufficient to maintain the charge on the 12V battery. You can’t, let me repeat that, can’t overcharge the HV battery. I’d actually recommend that you fully charge the battery once or twice a month. Cell balancing occurs as the battery reaches a full charge, which in the case of a Clarity is actually 90%.

I’ve left the car, unplugged for 4-6 weeks on at least 2 occasions. The 12V was not discharged on either occasion. As far as keeping the HV battery in the 40-60% SOC range, I believe it is futile unless you intend to will the batteries to your grandchildren.

 

[insightman]

You don't even have to drive a long distance. If you have a secure parking place (eg. garage), you can just turn the car On a half-hour before a 5-minute trip to the corner store and the traction battery will charge the 12-Volt battery.

 

[JFon101231]

Agree, think you just have a dying battery.
I left mine for 2 weeks and 3.5 weeks and it was fine when I came back.

 

[KyleH]

Did you measure the voltage during the red eye event? That window is frequently misread. If the car powers up, the battery is good.

I didn't. I should have. The car always powers up, and hasn't ever given a scare. But as much as the car sits idle, it's not surprising the battery was down a bit on voltage. After about 24 hours on the battery tender, it was back in good shape, showing the blue little eye again. I'd expect relative to a starter battery, these 12v batteries wouldn't give the signature audible indication of dropping voltage, and I fear obliviously driving around with a sub-par 12v, on the brink of being left stranded.

In my opinion, this is way too much work. A couple of brief drives a week should be sufficient to maintain the charge on the 12V battery. You can’t, let me repeat that, can’t overcharge the HV battery. I’d actually recommend that you fully charge the battery once or twice a month. Cell balancing occurs as the battery reaches a full charge, which in the case of a Clarity is actually 90%.

I get that the HV battery doesn't let you fully charge or deplete the capacity. However, based on my research, I've been working under the assumption more recently that the battery sitting in the 50% range is preferable to one sitting at (a registered) 100%. We do fully charge the battery when we are heading out on longer trips where we will be expecting to operate in hybrid mode, utilizing the EV primarily in town, and HV for the highway. I was not aware about the cell balancing only happening at the full(ish) charges. Is there any evidence or facts to indicate that this balancing is needed as certain intervals and/or that delaying would be harmful to the battery's long-term health?

I’ve left the car, unplugged for 4-6 weeks on at least 2 occasions. The 12V was not discharged on either occasion. As far as keeping the HV battery in the 40-60% SOC range, I believe it is futile unless you intend to will the batteries to your grandchildren.

I'll grant you it's anal, but as a Leaf owner, I'm pretty focused on doing what I can to maximizing the battery's life. Indeed likely doing a favor for the next owner.

 

[Landshark]

I'd expect relative to a starter battery, these 12v batteries wouldn't give the signature audible indication of dropping voltage, and I fear obliviously driving around with a sub-par 12v, on the brink of being left stranded.

You are correct that the 12V will not give the slow cranking warning that a dying starting battery would in a conventional car. The 12V battery in the Clarity powers up the system, it does not start the engine. Some owners have opted to carry a Lithium jump pack to combat fears of a dead 12V.

I was not aware about the cell balancing only happening at the full(ish) charges. Is there any evidence or facts to indicate that this balancing is needed as certain intervals and/or that delaying would be harmful to the battery's long-term health?

I’ll suggest that you research cell balancing on your own. I will only add that the Honda manual recommends fully charging the battery prior to each trip. And nowhere in the manual does it recommend operating the vehicle with the battery between 40-60% SOC.

Depending on where you live, you have an 8-10 year warranty on the battery. As designed, the car defaults to EV mode every time it is powered up. Without an intervention from the driver, it will fully deplete the battery before switching to HV mode. Then the battery will need to be (fully) charged. That’s how the Honda designed the car. I’m going with the theory that operating the car as designed won’t harm the battery.

 

[Frankwell]

In a post one month ago in a similar thread I mentioned that I was trying out an idea similar to what Kyleh did, which is to set a schedule to charge my HV battery for 30 minutes each day while I am out of town, so that the 12V battery will get daily charging.

https://www.insideevsforum.com/comm...12v-battery-bites-the-dust.12273/#post-149884

It was very easy to do, so I did the same thing on another one week trip that I just got back from. I use level 1, someone on level 2 who only has about two hours of charging time to spread out over the trip, they may need to set it to charge for 15 minutes per day, or maybe 10 minutes per day on a longer trip. But that still should be enough charging to keep the 12V topped up.

Now there is no way to prove either way whether doing this will actually help extend the life of the 12V battery. People have reported that their car sat for a week or even longer with no charging, and their car started up just fine. But just because the car started doesn't prove that the 12V battery didn't discharge an appreciable amount during the time that it sat. Especially since hybrids require so little 12V power to get started.

Someone may argue that if you have a healthy 12V battery, there is no way that sitting for a week without charging will have any affect on battery longevity. Maybe they are right, but I don't think that can be proven. Am I worried about it? No. But it's so easy to set a 30 minute charge session (or 15 minutes or whatever). I just set it once and it repeats automatically every night while I am on the trip. Also eventually my 12V battery will near the end of its life, which I probably won't know, and the 12V may not be be able to tolerate a week or two without charging, and I might come home to a dead battery. Am I worried about that? No, because I have a couple of portable jump starters, a glovebox size one, and a larger one that has higher capacity. I'm sure either one will get the car started in that situation. But again it's so easy to set the schedule that I will probably do that from now on when I go out of town. I do have a battery maintainer, but this seems even easier.

 

[Landshark]

Someone may argue that if you have a healthy 12V battery, there is no way that sitting for a week without charging will have any affect on battery longevity. Maybe they are right, but I don't think that can be proven.

A 12V battery, left to sit for a week in a parked car, will not self-discharge more than a few percent. That will not have a statistically meaningful impact on the longevity of the battery. You don’t have to take my word on this. The information is readily available.

A battery that discharges, in one weeks time, to a level that would have a detrimental impact on longevity, is a battery that either has a load that should be removed or is already damaged.

 

[Frankwell]

A 12V battery, left to sit for a week in a parked car, will not self-discharge more than a few percent. That will not have a statistically meaningful impact on the longevity of the battery. You don’t have to take my word on this. The information is readily available.

The article that you cut and pasted mentioned how discharge rate is affected by temperature, for example 4% per week at 80 degrees. But substantially less than that at moderate temperatures. That is interesting. I knew there would be a difference but I am surprised how large a difference temperature makes on discharge rate, as 80 degrees and higher is pretty normal temperatures in many parts of the country.

Encouraging to hear that studies have shown that this amount of discharge will not have any affect on battery longevity. The question I would have is whether this is true regardless of how often it occurs. If it only happens occasionally then I doubt if anyone expects any effect, at least I don't. But if it happens more often than that, is there a point where it might start to affect battery life? For example someone has a car that they drive only on weekends, that will result in maybe two hundred occurrences of a week's worth of discharging during the life of the battery. And depending on where they live many of those discharges will be 4% or more. That may be the less common situation, but not entirely implausible as some people may only drive their Clarity once a week. So apparently there are studies and longevity tests that have shown that 12V lead acid car batteries last just as long in those conditions compared to a battery that is charged more often? If you don't have an immediate link to such a study that's fine I'm not questioning it, I'm just wondering if the studies also indicate a point where the number of occurrences per year would effect a decision on whether to use a battery maintainer. I.e. discharging X% once every couple of months is okay, but if it happens say every other week that might start affecting battery life. Which again would seem to have temperature as a factor in that equation.

And it's also a matter of degree, i.e how much extra longevity are we talking about. If as an example studies indicated that in the OP's situation (car driven less than 20 minutes, once or twice a week), keeping the 12V battery charged daily would on average extend the life of the battery approximately two months. They might feel if it adds two months to the expected life of the battery then it is worth taking the easy step of setting a 30 minute (or whatever) charge schedule that repeats every day. Or they might say "Two months? Not worth even that amount of effort." Of course if studies indicated that daily charging would have no effect on longevity in their situation, then of course it's not worth even doing something easy since it would make no difference.

But maybe in a situation where temperatures are higher, and charging only occurs once a week, and if studies indicated that in that situation you may extend the life of your battery say 6 to 9 months, more people might think it's worth the effort of setting a daily short charge session. But again if studies show that it makes little or no difference in that situation, then it's not worth it. I am guessing however that such studies would also show where it would start to have an impact at a given temperature, say two weeks without charging, three weeks, four weeks, or whatever.

 

[Landshark]

I’ll suggest that you do your own research on the matter and then decide on a battery maintenance protocol that suits your needs.

 

[Frankwell]

I’ll suggest one last time that you do your own research on the matter and then decide on a battery maintenance protocol that suits your needs.

Wow. Not to worry I won't ask you any more questions about it. And anyway in my last post I was not talking about my situation, which I already indicated I don't have any needs or worries about, I was talking about the type of situations that other people might get into, since this topic is one that many people seem to be interested in. And by the way it wasn't me that you were telling to do my own research instead of asking you any more questions, you were telling that to KyleH in post #11. As far as I can tell this is my first warning, which I will certainly comply with.

 

[Landshark]

And by the way it wasn't me that you were telling to do my own research instead of asking you any more questions, you were telling that to KyleH in post #11. As far as I can tell this is my first warning, which I will certainly comply with.

You are correct.

It was a suggestion, not a warning, nor was it telling anyone what to do.

Perhaps your curiosity will motivate you to find the answers you seek though your own research.

 

[Hoon]

I just came back from a 3 week vacation and my 12V was dead measuring 2.6V. HV battery level had almost no changes staying at about 60%.

I had a ODB adapter plugged in which is probably what completely drained the 12V.
My 3A Battery Tender wouldn’t start charging as it can’t detect the 12V and plugging in the EVSE doesn’t start charging as the car computers need 12V to come up. I ended up connecting a jumper cable from my wife’s Mazda CX-5 which still measured about 12.3V after sitting in the garage for the same duration and after about 10 minutes the Clarity’s lead battery was measuring 12V. From there I switched over to the Battery Tender charger and was able to charge up all the way.

The moment I connected the jumper cable, the car alert was triggering so I had to quickly press the unlock button on the remote.
After fully charged, there were all these warnings and took a few minutes for the car to initialize everything.

I’m now considering buying a li-ion jumper battery pack.

Are there any AGM deep cycle battery for Clarity? Or is it a waste of money?

 

[Landshark]

Are there any AGM deep cycle battery for Clarity? Or is it a waste of money?

Yes, there are Group size 51 AGM’s available. AGM’s offer some advantages over FLA’s. However, they are still subject to premature death if allowed to become deeply discharged. In other words, it’s just as easy to kill a $200 battery as it is to kill a $100 battery.

 

[PHEV Newbie]

I just came back from a 3 week vacation and my 12V was dead measuring 2.6V. HV battery level had almost no changes staying at about 60%.

I had a ODB adapter plugged in which is probably what completely drained the 12V.
My 3A Battery Tender wouldn’t start charging as it can’t detect the 12V and plugging in the EVSE doesn’t start charging as the car computers need 12V to come up. I ended up connecting a jumper cable from my wife’s Mazda CX-5 which still measured about 12.3V after sitting in the garage for the same duration and after about 10 minutes the Clarity’s lead battery was measuring 12V. From there I switched over to the Battery Tender charger and was able to charge up all the way.

The moment I connected the jumper cable, the car alert was triggering so I had to quickly press the unlock button on the remote.
After fully charged, there were all these warnings and took a few minutes for the car to initialize everything.

I’m now considering buying a li-ion jumper battery pack.

Are there any AGM deep cycle battery for Clarity? Or is it a waste of money?

It would be less expensive to buy a $20 battery tender when the car is ever left undriven for more than a week at a time. As others have said, allowing a 12 v battery to get depleted is damaging to the battery. Unlike your traction battery (whose ideal state of charge is 50%), your 12 volt battery has the longest life if always kept fully charged.