My Clarity eats up 12V batteries

I think there were those who cut way back on driving during the past couple years. The parasitic current can discharge the battery if the car is not driven for a couple of weeks, and that is very hard on a battery. Another thing to be careful of is to NOT use accessory mode (by pressing the start button without having your foot on the brake). If you are sitting in the car operating things, this battery has a pretty low capacity and it can drain easily. Always start the car fully ("READY" mode). This charges the 12V battery from the HV battery while using accessories.

Wiith 35K miles on your car, you are driving it a fair amount so it's not likely that lack of use can explain this (unless there is something about your driving patterns that results in the car sitting idle for multiple weeks at a time). Have you added electrical devices that could have increased your parasitic battery drain?

Our car is very similar to yours (3.5 years, 33K miles) and it has never failed to start, still the original battery. I do carry a jump starter because of stories like yours, but have never needed to use it.

 

What region of the country are you? I have seen various maps like seen on this webpage, https://www.firestonecompleteautocare.com/blog/batteries/know-your-cars-battery/ showing that depending on where you live, batteries have different lifespans. I have had my share of battery replacements as I'm in one of the "red" zones in that map. Another thing that I have heard when talking to my local O'Reilly's parts person, the battery quality has seemingly declined in the last 5 or 6 years, too. Even in the premium quality battery brands, they get a significant portion returned in extremely short time frames. The numbers they were using were more than 10% of the batteries die in 60-180 days and another 25% in the first 18 months. I think there may be something to what they are experiencing as I had a battery (different car) that I replaced go out after 5 months of abnormally mild weather. I am definitely paying a bit more for batteries that have replacement guarantees for 2 or 3 years. Prorating after that is fine, but after Ford replaced a battery under warranty within the first year, and then the replacement battery only lasted 13 months, I can't even count on OEM replacements.

 

I'm still on the OEM 12v battery in my '18 Clarity that I bought new in March 2019. 16K miles, not a lot of miles as I don't have a long commute to work.

 

I'm still on my OEM 12V battery in my '18 as well. March 2018 build with purchase in late June of 2018. 35k miles. Will be interesting to see the life, but I carry a jump battery pack and jumper cables in the trunk as preparation for the inevitable end of it.

 

I'm also still on original battery. Built in November 2018, bought in December 2018, now with 27,700 miles on it.

 

Still on my original battery. 2018 clarity touring. Purchased July 2018. Live in very hot california desert. 23 k miles. Only had to jump it once: when I hadn’t driven it for a few weeks at the height of the pandemic. Otherwise battery is fine even after away on vacation for a week last month.

 

I do put my 12v on a Battery Tender every month or so and let it trickle charge overnight. Perhaps that helps, perhaps its just feeding my OCD. lol

 

In Western Oregon we don't often have sustained high temperatures. I presume that's the reason, but I've routinely had 12v batteries in cars exceed 10 years. The last battery in my 2004 Tundra was date-marked. The date mark was 11 years old. The battery worked fine, and tested fine, and I chose to replace it anyway. I don't want to find out when I'm on the mountain in snow that it's time to replace, but I don't replace batteries much. I've also never used a tender.

PS: I don't mean to brag. My meaning is this is definitely a "your mileage may vary" type of deal. My Clarity manufactured June 2018, new to me september 2018 has the original battery.

 

Get a premium battery. It’s worth it. Our Odyssey used to chew through batteries and we finally swapped it with a premium high capacity battery from O’Riley. Haven’t had a problem since. The Honda OEM battery wasn’t cutting it.

 

Define "premium"... You can't just assume it is better because it costs more.
Would you say that length of the warranty is indicative of how "premium" the battery is?

 

This is what we got for the Odyssey that seemed to finally stop the random low battery.

https://www.oreillyauto.com/detail/c/platinum/super-start-platinum-battery-group-size-47-h5/

Good question on warranty. Normally I would look at warranty length as an indicator of quality, but the battery would be randomly dead and still pass Honda’s battery spec and they wouldn’t replace it. Honda’s minimum spec didn’t seem to be covering it with how much we used the car.

If you want complete overkill, Jay Leno loves these batteries and puts them in 1920 cars that don’t even have a radio:

https://www.oreillyauto.com/detail/c/yellowtop/battery---accessories/batteries/31624da3221a/optima-yellow-top-post-battery/obt1/yel48/v/a/143556/automotive-van-2018-honda-odyssey?pos=7

 

I m in NJ, with a '18 and 30K. Still on the original batt. The only thing I can think of that can possibly affect the 12V batt is the heat from the engine. Batteries don't like heat. So maybe driving a lot in HV mode will shorten the 12v batt.

 

Could an OBD II device bleed power from a 12V battery when the car is off? Presumably not, but just tossing it out there.

 

It can...
The 12V power to the OBD II connector is always on.

The Vgate adapter that many have been using draws around 50 mA when it is on, but with it's default settings, the Vgate will turn itself off after maybe an hour. There is a command to make it 'always on', but I don't think many would do that.

The Clarity itself has a parasitic battery drain of around 100 mA and there is really nothing you can do about that. This 12V battery does not have a very high capacity and I think it be drained in less than 3 weeks if it just sits there idle.

 

I have 62k miles on my 2018, still the original battery. I just left it at the airport in the hot Florida sun for over 3 weeks and was pleasantly surprised that everything worked fine when I got back.

 

My 2018 Clarity has 46,000 miles and is still on the original battery. While I have had no problems, it's on my mind to pre-emptively replace it. Based on past vehicle experience, I seem to be on bonus time after just over four years. Maybe standard ICE vehicles are not a good comparison.

 

Perhaps you could carry one of those compact jump-starters with you and delay replacing your working battery until the first time it hiccups and needs a jump-start. That said, I replaced mine pre-emptively after 4 years rather than worry about it.