Hybrid T4R6G: Tapping off the Rear 12V Battery

[Farzad_k]

Hi.

On my 2025 Hybrid (TRD OR), I plan on tapping off the rear 12V battery using a REDARC DC-DC charger to charge a LiFePO battery while the car is in the Ready mode.

On the rear 12V battery positive terminal there are 4 wires that go out, presumably to power 4 or more accessories. They are fused 7.5, 7.5, 15 and 15 amps.

There is a big gray cable that attaches to that terminal. I am assuming this cable brings charging power to the 12v battery from a built-in DC-DC converter. And there is one bolt without a nut, and I don't know what it is for.

My plan is to tap from the bolt I have circled in the picture so that I don't disturb the connectivity of the accessories while I do this. But should I actually disconnect those fuses or unplug the accessory cable altogether?

Anyone knows much about these cables/wires and any risk of handling them?

Thanks a lot.

Farzad

 

[stellarbuilt]

The four fused wires on the rear 12-volt post are factory accessory feeds and should not be disconnected. The large gray cable is the main charge line from the hybrid DC-DC converter. Leave all of that exactly as it is. The unused stud on the battery terminal is Toyota’s auxiliary upfitter post. That’s the correct place to tap your REDARC input so you don’t disturb any factory wiring. Just add your own nut, fuse your line close to the battery, and run it to the charger. No special hybrid risks as long as the truck is off, you disconnect the negative before working, and you don’t open or remove the factory-fused leads.

 

[Farzad_k]

The four fused wires on the rear 12-volt post are factory accessory feeds and should not be disconnected. The large gray cable is the main charge line from the hybrid DC-DC converter. Leave all of that exactly as it is. The unused stud on the battery terminal is Toyota’s auxiliary upfitter post. That’s the correct place to tap your REDARC input so you don’t disturb any factory wiring. Just add your own nut, fuse your line close to the battery, and run it to the charger. No special hybrid risks as long as the truck is off, you disconnect the negative before working, and you don’t open or remove the factory-fused leads.

Thank you for your help.

I understand that the built-in DC-DC converter acts like smart alternators that only work when needed to keep a certain battery charged.

According to REDARC, the charger will only draw when it finds a source with 12.8v or higher. This means the REDARC may draw from the rear 12v battery until its voltage drops to the level that triggers the internal DC-DC converter to come back on to top off the rear 12v. I don't know what that trigger point might be, and I wonder if adding more work to the internal DC-DC converter may have long term consequences on the longevity of the traction battery.

What are your thoughts, and do you know of a technical source for the functioning of the internal converter?

Thanks a lot.

Farzad

 

[ekko4r]

Following, hope you do pictures after youre finished!