Recent Software Update

[k1m]

Our trucks not keeping their 12v batteries charged is probably why they added an alternator to hybrids for the 2025 model year. Toyota must have realized that keeping the battery charged with just the motor/generator was not enough, but what about those of us who bought 2024 hybrids without an alternator?

I’ve been watching my battery gauge (on the in dash gauges) drop more frequently while operating my TRD Pro. I ended up putting a meter on it and it shows that when the battery gauge drops the 12v voltage is only at 12.8v. When the in dash gauge shows as halfway between the 9v and the 19v it is at 14.4. After I start the truck it will sit at 14.4 (occasionally even hitting 14.8) and then inevitably it drops to the 12.8. Typically sitting overnight it stays up longer. Sometimes it will bounce back up for a while. I had a ham radio wired to the battery but I pulled it long ago thinking that was the issue; it wasn’t. I’m not sure what dictates the charging circuits level but something feels amiss. I haven’t found anyone else talking about it online.

Sponsored

 

[TacoFreak]

I’m not sure what dictates the charging circuits level but something feels amiss. I haven’t found anyone else talking about it online.

I don't think that any of us thought much about this until we realized that Toyota added alternators to most 2025 hybrids. Your analysis shows that our batteries are not being kept at the proper levels all of the time.

The 12v battery can only be charged by the motor/generator in 2024 models. So anytime the truck is not moving there won't be any charging, and anytime the M/G is adding power it isn't charging either. So that just leaves regen periods, which obviously are not enough to always keep the battery fully charged. That is almost certainly why Toyota added an alternator to 2025 hybrids.

 

[k1m]

I don't think that any of us thought much about this until we realized that Toyota added alternators to most 2025 hybrids. Your analysis shows that our batteries are not being kept at the proper levels all of the time.

The 12v battery can only be charged by the motor/generator in 2024 models. So anytime the truck is not moving there won't be any charging, and anytime the M/G is adding power it isn't charging either. So that just leaves regen periods, which obviously are not enough to always keep the battery fully charged. That is almost certainly why Toyota added an alternator to 2025 hybrids.

This is what my biggest concern is, it isn’t set to charge like it was on an alternator, that makes sense as it is a different system design; the question is does it keep the 12v battery at a set voltage level and that is up to the system programing?
Based on what I saw from the voltage levels the inverter seems to pull off the hybrid battery (as it maintains that 14.4 for a period of time initally) then it cuts it back. Is this once it sees a voltage that the software considers charged? That is the conclusion I have come to but I don’t feel comfortable with that conclusion. Alternators tend to slowly ramp back but stay at 13.8 for the rest of the ride.
Is our Tacomas like this because the hybrid battery obviously isn’t recharged unless the motor is in the generate mode and they are trying to keep as much juice on tap for the on demand torque?
I would love an expert speak up and ease the concerns.

 

[Ron]

I think the alternator in the 2025s is a workaround for a design flaw in the DC power module. It's not working as intended and its too expensive to fix - or they cant get it fixed quick enough to keep the assembly line running.

 

[TacoFreak]

@Ron that is interesting. I wonder if that might also be part of why 4th gen hybrids seldom achieve their EPA mileage numbers. Did Toyota, the masters of hybrid tech, manage to screw the pooch on this drivetrain? And what about owners of 2024 hybrids? Toyota obviously added the alternator to address some problem which could not be fixed in software.

 

[Ron]

@Ron that is interesting. I wonder if that might also be part of why 4th gen hybrids seldom achieve their EPA mileage numbers. Did Toyota, the masters of hybrid tech, manage to screw the pooch on this drivetrain? And what about owners of 2024 hybrids? Toyota obviously added the alternator to address some problem which could not be fixed in software.

If the DC module is not working as expected, maybe they had to use less aggressive hybrid algorithms to save DC juice (and burn more gas).

Im just speculating but it smells like that kind of pile.

 

[StreeTaco]

The 12v battery is maintained by the Hybrid battery. The hybrid battery is charging anytime the ICE is running, except on acceleration or low speed EV travel. The battery can charge while in park, it doesn’t need to be moving or braking to charge.

 

[StreeTaco]

Where are all the IForce Max owners with defective or dead 12v batteries?… Roll Call

 

[Baltimore]

Where are all the IForce Max owners with defective or dead 12v batteries?… Roll Call

Zero issues so far and I'll go days between driving

 

[BoboForShort]

@Ron that is interesting. I wonder if that might also be part of why 4th gen hybrids seldom achieve their EPA mileage numbers. Did Toyota, the masters of hybrid tech, manage to screw the pooch on this drivetrain? And what about owners of 2024 hybrids? Toyota obviously added the alternator to address some problem which could not be fixed in software.

As far as I have seen the alternator has only been added to the 2025 trucks that have the AUX switches. The 2025 has 4 unlike the 24 that only has 3.

Seeing as how they only added it along with the AUX packages and not to all 2025s I'd be willing to bet they're more concerned about instantaneous power draw and not some scourge of 2024s that can't keep their battery charged.

 

[soupy1234]

I’ve been watching my battery gauge (on the in dash gauges) drop more frequently while operating my TRD Pro. I ended up putting a meter on it and it shows that when the battery gauge drops the 12v voltage is only at 12.8v. When the in dash gauge shows as halfway between the 9v and the 19v it is at 14.4. After I start the truck it will sit at 14.4 (occasionally even hitting 14.8) and then inevitably it drops to the 12.8. Typically sitting overnight it stays up longer. Sometimes it will bounce back up for a while. I had a ham radio wired to the battery but I pulled it long ago thinking that was the issue; it wasn’t. I’m not sure what dictates the charging circuits level but something feels amiss. I haven’t found anyone else talking about it online.

"Smart" alternator. Drops the voltage when the load drops to save a smidgin of fuel.

From https://www.etrailer.com/question-326099.html

How to Determine if Vehicle Has Smart Alternator for Using REDARC Battery Charger

1. Locate your main vehicle battery​

2. Start the engine, ensuring any fans, radio, lights etc. are turned off.​

3. Take a voltage reading across the main vehicle battery​

4. Leave running for around 5/10 minutes, then repeat step 3​

​

If your readings are around 14.4V DC then then you most likely have the traditional, non-smart alternator.​

If your reading is closer to 12.5-13.5V then it’s likely that you have a smart alternator. A 2013 model most likely would not have a smart alternator.​

Sponsored