12V battery problems 24 TrailHunter

[TacoFreak]

I'm the opposite...I don't think I'll ever buy a non-hybrid!

I agree! I said that I wouldn't buy a hybrid before I realized that some non-hybrid Toyotas have the same problem with charging their batteries. Some people think it might be related to improving Toyota's CAFE numbers. I love the hybrid drivetrain and since the charging problem exists for non-hybrids also, I would definitely get another hybrid.

My issue with the charging is that the problem is not just with short drives. No matter how much I drive my truck the 12V always settles to 12.1-12.2 volts resting state of charge. I can make a round trip of 200-300 miles and it will still be at 12.2 volts or lower. That is around 50% charged and will kill a battery that is not deep discharge capable. That level is 15 minutes after shutting the truck off, and then with all of the parasitic drains it will get low enough to not even turn on if it sits for very long.

I charge mine with a maintainer, so I know that the battery can be fully charged. If I do that for a few days every week it settles in at around 12.5 volts. A deep discharge battery should fix that problem, although my wife's battery electric SUV's 12 volt discharges to the point where the car won't even turn on unless I put it on my maintainer from time to time.

Since some trucks seem to keep their batteries charged to a higher level, so I think something is wrong with my truck. But the dealers just tune you out when you ask about battery charging and say buy a trickle charger. They should at least update their BS to tell us to buy a maintainer. lol

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[shackley]

I agree! I said that I wouldn't buy a hybrid before I realized that some non-hybrid Toyotas have the same problem with charging their batteries. Some people think it might be related to improving Toyota's CAFE numbers. I love the hybrid drivetrain and since the charging problem exists for non-hybrids also, I would definitely get another hybrid.

My issue with the charging is that the problem is not just with short drives. No matter how much I drive my truck the 12V always settles to 12.1-12.2 volts resting state of charge. I can make a round trip of 200-300 miles and it will still be at 12.2 volts or lower. That is around 50% charged and will kill a battery that is not deep discharge capable. That level is 15 minutes after shutting the truck off, and then with all of the parasitic drains it will get low enough to not even turn on if it sits for very long.

I charge mine with a maintainer, so I know that the battery can be fully charged. If I do that for a few days every week it settles in at around 12.5 volts. A deep discharge battery should fix that problem, although my wife's battery electric SUV's 12 volt discharges to the point where the car won't even turn on unless I put it on my maintainer from time to time.

Since some trucks seem to keep their batteries charged to a higher level, so I think something is wrong with my truck. But the dealers just tune you out when you ask about battery charging and say buy a trickle charger. They should at least update their BS to tell us to buy a maintainer. lol

My 2026 TH has an alternator, and so far (built December 2025) the battery is holding. Are most of the problems due to the earlier TH not having an alternator? I know this has been discussed, but I'm wondering. I plan on getting a deep discharge battery at about 1 years. I'm retired and don't always drive any distance much of the time, but use a maintainer. It sat for 9 days and the battery was at 12.3-12.4 when I got home, but had it on a maintainer when we left 9 days earlier.

 

[TacoFreak]

My 2026 TH has an alternator, and so far (built December 2025) the battery is holding. Are most of the problems due to the earlier TH not having an alternator? I know this has been discussed, but I'm wondering. I plan on getting a deep discharge battery at about 1 years. I'm retired and don't always drive any distance much of the time, but use a maintainer. It sat for 9 days and the battery was at 12.3-12.4 when I got home, but had it on a maintainer when we left 9 days earlier.

A lot of us assumed that they added the alternators to fix the charging problem, but a number of people complaining about charge levels have newer trucks with them. Toyota indicated that they added the alternator to support the 4th aux output. Some non-hybrids, which obviously have alternators have the same issues.

I have given up trying to figure it out partly because other than this I love my truck. So I put it on a maintainer on a regular basis, I will get a deep discharge battery when the OEM one dies, and I carry a jump pack so I can't get stranded. I obviously really like the truck or I wouldn't go through all of that rather than just sell it and move on.

 

[shackley]

A lot of us assumed that they added the alternators to fix the charging problem, but a number of people complaining about charge levels have newer trucks with them. Toyota indicated that they added the alternator to support the 4th aux output. Some non-hybrids, which obviously have alternators have the same issues.

I have given up trying to figure it out partly because other than this I love my truck. So I put it on a maintainer on a regular basis, I will get a deep discharge battery when the OEM one dies, and I carry a jump pack so I can't get stranded. I obviously really like the truck or I wouldn't go through all of that rather than just sell it and move on.

As I mentioned in another post, our 2023 RAV 4 Prime PHEV has the same problem.

 

[Porwal22]

As long as you have the room to install one, buy a battery disconnect post. They work great, and you never have to carry tools.

https://m.media-amazon.com/images/I/51JgRJK7oLL._AC_SL1200_.jpg

 

[shackley]

As long as you have the room to install one, buy a battery disconnect post. They work great, and you never have to carry tools.

https://m.media-amazon.com/images/I/51JgRJK7oLL._AC_SL1200_.jpg

Something useful when going away for a time.

 

[Porwal22]

Something useful when going away for a time.

Yes. I can’t see it where it’d be useful on a daily driver. If you were not driving your truck for two or more weeks, then it’s a good idea.

 

[ColoradoBoo]

This thread got me wondering about our two hybrids in the garage...wife's 2024 Corolla Hybrid and my 2021 Prius AWD.

So, on Saturday, tested both the 12-volts.....Corolla was at 65% and saying it needs to be recharged. (Not surprising, hasn't been driven much the past week) What REALLY surprised me was what my Prius said....at 80% charge! WHAT? I'd driving it 4 out of 5 days to work and it's a 90 mile roundtrip.

So plugged in the Battery Tender to each and removed it when the green light came on....both tested to 100% full.

Didn't take either cars anywhere Sunday (we took the Tundra up into the mountains) and I had some time before work, Monday morning, so tested both again and both were at 85% and 87% full.....that's not a good sign. Is our draw, when parked, really that much??

So I don't know if it's these cheap OEM batteries Toyota is putting in their cars or not. They aren't TrueStart batteries so I might have to just replace both soon and keep an eye on them.

 

[TFOUTS]

That is an interesting development. In 48 hours down 15%.

 

[TacoFreak]

So, on Saturday, tested both the 12-volts.....Corolla was at 65% and saying it needs to be recharged. (Not surprising, hasn't been driven much the past week) What REALLY surprised me was what my Prius said....at 80% charge! WHAT? I'd driving it 4 out of 5 days to work and it's a 90 mile roundtrip.

I have it in writing from my dealer's service department that my truck is fine and that the problem is that I don't drive it enough. So Toyota does not plan to address this and we are on our own in figuring out a solution.

That is an interesting development. In 48 hours down 15%.

Yes it is interesting. No matter how much I drive my truck after a few days the battery is always at less than 50% charged. Of course the truck is fine and the problem is me for not using it as Toyota intended. They warn you about everything else that can go wrong, so where is the warning about the minimum number of miles you need to drive on a daily basis to keep your hybrid alive?

 

[GSPHerder]

Yes it is interesting. No matter how much I drive my truck after a few days the battery is always at less than 50% charged.

Has your vehicle ever not started? Im lucky if i drive mine every 4 days, sometimes upto 6 days and it always starts. I started out with volt meter and and charger and was suprised about the resting volts as you mention. When Im driving the cobb access port shows 14.1 volts in the system. Initially I was concerned but it has never failed to start and I do carry the jump pack so now I just dont worry about it anymore.

 

[TacoFreak]

Has your vehicle ever not started?

No, it has never failed to start. Partly because I am aware of the problem and I charge it before it won't turn on - once it gets down to 12 volts or so. Once the electronics turn on it uses the DC/DC converter and the voltage is the normal 14.1 volts. If the electronics turn on it will start, because the starter is powered by the traction battery.

But my wife has a 2023 Lexus BEV and it has several times run its 12V down to where it won't even turn on, which is why I keep both of them charged with my battery maintainer and both vehicles have a jump pack just in case I screw up and let it go completely dead. The first time her SUV went stone dead the jump pack was in the hatch and you can't open it with a physical key. So I had to put it on my maintainer long enough to get it to turn on and that let me open the hatch.

I have had 10-20 year old Toyota products that never failed to start, so to say the least this mess is disappointing.

 

[shackley]

No, it has never failed to start. Partly because I am aware of the problem and I charge it before it won't turn on - once it gets down to 12 volts or so. Once the electronics turn on it uses the DC/DC converter and the voltage is the normal 14.1 volts. If the electronics turn on it will start, because the starter is powered by the traction battery.

But my wife has a 2023 Lexus BEV and it has several times run its 12V down to where it won't even turn on, which is why I keep both of them charged with my battery maintainer and both vehicles have a jump pack just in case I screw up and let it go completely dead. The first time her SUV went stone dead the jump pack was in the hatch and you can't open it with a physical key. So I had to put it on my maintainer long enough to get it to turn on and that let me open the hatch.

I have had 10-20 year old Toyota products that never failed to start, so to say the least this mess is disappointing.

No, it has never failed to start. Partly because I am aware of the problem and I charge it before it won't turn on - once it gets down to 12 volts or so. Once the electronics turn on it uses the DC/DC converter and the voltage is the normal 14.1 volts. If the electronics turn on it will start, because the starter is powered by the traction battery.

But my wife has a 2023 Lexus BEV and it has several times run its 12V down to where it won't even turn on, which is why I keep both of them charged with my battery maintainer and both vehicles have a jump pack just in case I screw up and let it go completely dead. The first time her SUV went stone dead the jump pack was in the hatch and you can't open it with a physical key. So I had to put it on my maintainer long enough to get it to turn on and that let me open the hatch.

I have had 10-20 year old Toyota products that never failed to start, so to say the least this mess is disappointing.

I wonder if there is any data on the difference between the THs that have an alternator, and those that do not (i.e. late 2025-2026) versus 2024? As I mentioned before our 2023 RAV4 Prime PHEV lost the first battery in the first year and so we carry a NOCO at all times in both vehicles.

 

[TacoFreak]

I wonder if there is any data on the difference between the THs that have an alternator, and those that do not (i.e. late 2025-2026) versus 2024? As I mentioned before our 2023 RAV4 Prime PHEV lost the first battery in the first year and so we carry a NOCO at all times in both vehicles.

Yep, that kind of data would probably give us a better idea of what is going on. The only thing that I can add is that some people with alternators are still having their batteries get to very low voltages and fail to start. They have the same issues with parasitic drain when they are not driven regularly also.

I think the alternators are to support the 4th AUX and the batteries are still charge by the DC/DC converter, just like the earlier 4th gens. AFAIK Toyota has never clarified any of this, because their official story is that our trucks are actually fine. Their story is shut up and buy a maintainer or move on. When I am ready to let go of my truck I may very well do that.

 

[shackley]

Yep, that kind of data would probably give us a better idea of what is going on. The only thing that I can add is that some people with alternators are still having their batteries get to very low voltages and fail to start. They have the same issues with parasitic drain when they are not driven regularly also.

I think the alternators are to support the 4th AUX and the batteries are still charge by the DC/DC converter, just like the earlier 4th gens. AFAIK Toyota has never clarified any of this, because their official story is that our trucks are actually fine. Their story is shut up and buy a maintainer or move on. When I am ready to let go of my truck I may very well do that.

Yeah, my guy at the local dealer has been trying to find out from corporate with no luck. I'm not an auto electrician, but why wouldn't they use the alternator for the entire electrical system?

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