12v battery (hybrid) runs low after sitting for a week

[Bravada]

Before commenting on your post and to avoid misunderstandings, I want to add the following:
I do not know what you are doing, and I do not know what the acronyms you use mean. Still, I own a Trailhunter. It has close to 6000 miles now but, when it only had 340, I decided to take a long trip abroad and left it in a covered parking for 9 weeks, and it started the same as if I had only been gone 24 hours.
It does not have an alternator but it does not appear to need one.
Hope this helps you.

I've thankfully never had a no start condition either, knock on wood.
But I've noticed the low SOC, state of charge, as shown in a percentage on the conventional 12V battery. NOCO is a brand of smart charger. I was regularly seeing below 50% SOC shortly after driving it with a tester, as others in this post have reported. While I've not had any issues due to the low SOC, it's not good for the battery health long term. The picture below was approximately an hour after parking it from running errands a few weeks ago.

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[Vidman]

My truck will sit for 4-5 weeks in my shop and will start right up no problem

 

[crepr12]

Parked for 8 days zero issues as it should be...

 

[TacoFreak]

Parked for 8 days zero issues as it should be...

My truck starts after being parked for a week or so, but the 12 volt will not last long because the hybrid charging systems keeps my battery at only 12.0-12.2 volts. So it is fine because it starts from the hybrid battery, but no battery will last long if kept at the low of a state of charge.

At the very least I expect to have to replace the battery frequently and will move to an Optima the first time I have to buy the replacement. I also carry a jump pack because at some point the 12 volt will be so low that it will simply not start, even from the traction battery.

 

[Cordoc]

I've thankfully never had a no start condition either, knock on wood.
But I've noticed the low SOC, state of charge, as shown in a percentage on the conventional 12V battery. NOCO is a brand of smart charger. I was regularly seeing below 50% SOC shortly after driving it with a tester, as others in this post have reported. While I've not had any issues due to the low SOC, it's not good for the battery health long term. The picture below was approximately an hour after parking it from running errands a few weeks ago.

Ok,now I see what you are doing.
My knowledge of bateries is not great but it was aquired during my 9 years on a sailboat with my wife during which time we put 45690 miles and a circumnavigation.
I had a generator and never used the boat's engine for charging.
Based on that experience, I feel you have a defective battery and you should take your info to the dealer for a replacement.
Good luck and let us know.

 

[TacoFreak]

There are really only two answers that make sense. Either Toyota installed a lot of defective batteries in our trucks, or batteries are failing because they are not being kept properly charged.

Once I get a new battery I will still monitor the state of charge in my 12 volt to see which of these it is. My money is on my second theory, although I hope I am wrong.

 

[Bravada]

My truck starts after being parked for a week or so, but the 12 volt will not last long because the hybrid charging systems keeps my battery at only 12.0-12.2 volts. So it is fine because it starts from the hybrid battery, but no battery will last long if kept at the low of a state of charge.

At the very least I expect to have to replace the battery frequently and will move to an Optima the first time I have to buy the replacement. I also carry a jump pack because at some point the 12 volt will be so low that it will simply not start, even from the traction battery.

This is the exact reason I'm sharing what my battery is up to, I'm not alone. Even if it's a defective battery, the low charge would kill it anyway prematurely.

 

[TacoFreak]

This is the exact reason I'm sharing what my battery is up to, I'm not alone. Even if it's a defective battery, the low charge would kill it anyway prematurely.

My battery maintainer will charge the 12 volt to 100%, but as I drive my truck it slowly comes back down to 12.2 volts or less. It even went below 12.0 volts once but it still turned on and started, and that is when I put the maintainer on it. I think the DC-DC converter must be a poor design because there should be plenty of power in the hybrid battery to keep the 12 volt fully charged.

 

[Bravada]

My battery maintainer will charge the 12 volt to 100%, but as I drive my truck it slowly comes back down to 12.2 volts or less. It even went below 12.0 volts once but it still turned on and started, and that is when I put the maintainer on it. I think the DC-DC converter must be a poor design because there should be plenty of power in the hybrid battery to keep the 12 volt fully charged.

Add in the mystery that they added an alternator to '25MY, makes one think there is some more information we are not privy to. Likewise I'm curious if a higher quality battery would react differently, but I doubt it since the issue is the battery charge voltage.

 

[TacoFreak]

Add in the mystery that they added an alternator to '25MY, makes one think there is some more information we are not privy to. Likewise I'm curious if a higher quality battery would react differently, but I doubt it since the issue is the battery charge voltage.

Another forum member has a 2025 Pro that goes completely dead if parked for more than a week, and it has an alternator! His dealer told him that is normal and he should use a charger when he lets it sit for a week or more. It would not be dead in a week if his truck could keep the 12 volt fully charged.

So I have no idea what is going on, but something clearly is. I will get an Optima when I buy my first replacement battery. They are great batteries and a yellow top will tolerate a deep discharge without dying. For now I just keep a lithium Ion jump pack in the glove box for whenever it goes down to where it won't even turn on.

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