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

[TacoFreak]

Here is the reading this morning after about an hour of mixed city/freeway driving. I was stopped a light and the engine was off, but it read the same when the engine was on. I assume that is below what it should normally be, and my multimeter pegs it at 12.18 vdc. I have not put my maintainer on my battery yet, but I will do that soon and see if the battery can be charged to a higher level.

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[MustardTiger]

@TacoFreak 12.18v is way too low, and sadly my gauge shows the same position after driving for a bit. And it has had the battery replaced when it was new on the lot. I very much think Toyota is aware of the issue, hence some models now appearing with alternators. A TSB is in the works, it has to be. A battery will not last long being maintained at such low voltage.

 

[TacoFreak]

@MustardTiger Thanks for the feedback. I have my CTEK maintainer on it now. It labels a battery with that charge level as "bad" and is attempting to charge it. If it can't raise the charge level then the battery is already bad, and if it can then the truck is clearly not doing the job.

That is interesting about a battery failing when being maintained at such a low level. Dealers replace the bad batteries, but did they fail because the trucks can't keep them charged? That is what I think and that is why Toyota added alternators on some 2025 hybrids. Some people think it was just a bad batch of batteries, but I think this problem is actually caused by the truck.

@Tom Sellick's dealer told him that this was all normal, which is clearly a lie. The dishonesty and incompetence of some dealers is beyond belief. I think I have a good one but I guess I am about to find out.

 

[max911]

Crap quality batteries aren't just a Toyota thing.
In the last couple of years I have seen several batteries replaced on our fleet Fords that were less than two years old. In every case it was the battery's fault, not the truck's.
I had my Noco trickle charger on mine overnight. Might have put just a bit more charge into the battery than the alternator, but within a few days I had to get the booster pack out again.

 

[MustardTiger]

@max911 but your truck is good now since the battery change, right?

 

[gpburdell]

That is interesting about a battery failing when being maintained at such a low level. Dealers replace the bad batteries, but did they fail because the trucks can't keep them charged? That is what I think and that is why Toyota added alternators on some 2025 hybrids. Some people think it was just a bad batch of batteries, but I think this problem is actually caused by the truck.

Help me understand the thought here...

If Toyota thinks it's caused by the truck, and an alternator fixes it, why aren't they adding one to all hybrids instead of just the ones with a 4th AUX switch - which seems to be just the Pro and Trailhunter trims?

 

[TacoFreak]

Help me understand the thought here...

If Toyota thinks it's caused by the truck, and an alternator fixes it, why aren't they adding one to all hybrids instead of just the ones with a 4th AUX switch - which seems to be just the Pro and Trailhunter trims?

I can't really help because it does not make sense to me either. Everything you say points to the alternator being added just to support that 4th AUX switch.

So the problem might be the battery and not the truck's charging system, which would be my preferred outcome. They could give me a new battery and we would be done with minimal work on my truck. That is how it worked for @max911 and I hope that works for me too.

But my truck does not keep my battery charged above 12.2 volts and in three hours my battery maintainer has raised it to 13.32 volts. That tells me that the battery might be fine and the truck is the problem. I will leave the maintainer on overnight and grab a reference screenshot tomorrow of the final voltage after external charging. Then I will drive it for a while and see where it settles. I will report back on what I find.

I work in software at a company where we design and produce complex electrical/mechanical systems. It would have been expensive for Toyota to add that alternator with the hardware and software changes plus all of the re-engineering, testing and approvals. It does not make sense to me that they would do that just for one more AUX switch, but that is just my guess.

 

[max911]

@max911 but your truck is good now since the battery change, right?


Yes, it has performed flawlessly.
That includes it firing up after sitting for ten days.
The voltmeter stays at 14V all of the time now.

 

[ORHV]

Here is the reading this morning after about an hour of mixed city/freeway driving. I was stopped a light and the engine was off, but it read the same when the engine was on. I assume that is below what it should normally be, and my multimeter pegs it at 12.18 vdc. I have not put my maintainer on my battery yet, but I will do that soon and see if the battery can be charged to a higher level.

Same over here. My reading shows the same almost all of the time. Occasionally it will move up to ‘mid battery’ for a short period, then back down to the same as in your pic. Dealer said “this is normal.”
Battery appears ‘good’ but not being charged!

 

[TacoFreak]

Same over here. My reading shows the same almost all of the time. Occasionally it will move up to ‘mid battery’ for a short period, then back down to the same as in your pic. Dealer said “this is normal.”
Battery appears ‘good’ but not being charged!

Strange. Our trucks keep their batteries at a level that pretty much everyone says is too low but there is no problem? I don't understand.

My maintainer charged the battery to 13.32 and it just continues to charge without the battery going any higher. The maintainer is getting hot and I took it off for now. It will be interesting to see where it is tomorrow.

I will call the dealer soon and get an appointment. My truck is due for the trailer blind spot monitor calibration anyway and they can check out the battery then too.

 

[Jt2024]

My truck does quite a bit of sitting in the garage, as I'm away for longer periods of time. I've been monitoring the state of the 12v battery...and after returning a week later, I unlock truck and open hood...let things settle for 15 mins...and battery shows 12.0v. I feel it should be at least 12.5-12.6 (like 80-85% charge). Before driving it, I connect a 7.5 amp NOCO charger and let it complete a charge cycle. The truck has never not started for me however.

A couple things to note:

-my truck was delivered in the dead cold of winter, it was like -30c temps. The day I went to purchase, it was out on the lot, -35c...they just started it...immediately backed up through a snow bank and into the shop.
-it had been sitting on the dealer lot for about 1 month (in said cold temps) before I seen it and purchased
-after getting it home, I noticed the little red flip cover on the boosting terminal was broken at the hinge...and it was obvious booster cables had been attached at some point, maybe during transport? hard to say

Maybe...my battery was in a very low state of charge for an extended period, in freezing temps, prior to me buying it, and it either froze or lost a significant amount of life/amps

Anyone else have a 12v issue like this? Particularly the drain after sitting for more than 5 days?

I had the battery discharge after sitting for a week. Took it to dealer and they charged it and no issues since. Might sound strange but I had the Toyota APP Running a dread in some forums that there is a draw. I turned off (signed out) after the battery went dead and no issues yet.

 

[gpburdell]

But my truck does not keep my battery charged above 12.2 volts and in three hours my battery maintainer has raised it to 13.32 volts. That tells me that the battery might be fine and the truck is the problem. I will leave the maintainer on overnight and grab a reference screenshot tomorrow of the final voltage after external charging. Then I will drive it for a while and see where it settles. I will report back on what I find.

I work in software at a company where we design and produce complex electrical/mechanical systems. It would have been expensive for Toyota to add that alternator with the hardware and software changes plus all of the re-engineering, testing and approvals. It does not make sense to me that they would do that just for one more AUX switch, but that is just my guess.

Given the hybrids have a 2400W inverter, they certainly should have the capability to keep a battery charged.

Pure speculation but perhaps there's a batch of faulty voltage converters driving the 12VDC system from the 288VDC hybrid system? Rest of the stuff would be fine operating at 12.2VDC but it wouldn't have the battery at full capacity.

Time will tell.

 

[TacoFreak]

Given the hybrids have a 2400W inverter, they certainly should have the capability to keep a battery charged.

Definitely!

Pure speculation but perhaps there's a batch of faulty voltage converters driving the 12VDC system from the 288VDC hybrid system? Rest of the stuff would be fine operating at 12.2VDC but it wouldn't have the battery at full capacity.

Time will tell.

Yeah, it could be a bad voltage converter and I guess it could be the battery itself. I am letting it sit overnight to see what the battery does without any obvious load to draw it down. My schedule has been really busy but is opening up some now, so I hope to let the dealer check it out soon.

 

[MustardTiger]

I guess my thoughts on the alternator and 4th aux switch…this tells me the tipping point of needing an alternator is already very close on the trucks without the 4th aux switch…

 

[EVOTACO]

I have an OBD Link dongle that I can use to monitor various parameters. When I am in P, R, or N, I will see the voltage indicator above reading at the halfway point (5 segments) and voltage at the OBD port is 13.7 to 14.1. Once I select D, the voltage indicator shows the same as above (3 segments) and the reading at the OBD port is 12.7-12.9.

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