What I learned from my 12V battery swap

[Throwdown]

Nice write up OP, them are some teeny batts, that's why there are two.

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[ImAI]

2. The Rivian batteries are just cheap sealed lead acid batteries. 12V 18ah. I've got a ton of them laying around I use on my race cars. They are the exact same, probably all made in the same factory (hah). Size, ah, post locations & thread size...everything. See pics, sorry the Rivian one is fuzzy (I deleted the wrong image).

unless you show the justification for word cheap because you were able to cross check the part numbers against a database that compares all the other vendors and how they sourced their batteries from OEMs, i would not use word "cheap" as the rest of your bullet points are then marred with a negative connotation, ie. you lost the trust of a reader by skipping providing the details.

 

[Throwdown]

unless you show the justification for word cheap because you were able to cross check the part numbers against a database that compares all the other vendors and how they sourced their batteries from OEMs, i would not use word "cheap" as the rest of your bullet points are then marred with a negative connotation, ie. you lost the trust of a reader by skipping providing the details.

I don't think he meant it like screw rivian they use cheap batteries, but sealed lead acid batteries in my experience are the cheapest option for a vehicle, especially evs. Every ev and hybrid I work on has either AGM or Lithium batteries as their 12v system. Lithium LiFePo batteries work the best for their size because of their energy density, but they aren't without their own issues especially when the battery sensor is part of the battery and not replaceable separately. I was told that the rivian had AGM batteries OP just showed otherwise. Had they been AGMs most of them would have been able to be recovered.
Separate from this I call BS that one is for the right side and one for the left side of the vehicle, it likely just has two in parallel for combined power. Old 911s did the same thing but it was more for weight distribution, one small 12v in the LF and one small one in the RF corner of the car.

 

[Jayhawkeye]

Would better batteries result in less 12v issues I assume?

 

[Kuro-Rivian]

unless you show the justification for word cheap because you were able to cross check the part numbers against a database that compares all the other vendors and how they sourced their batteries from OEMs, i would not use word "cheap" as the rest of your bullet points are then marred with a negative connotation, ie. you lost the trust of a reader by skipping providing the details.

Wtf...I'm not even sure how to respond. Except to say take your thesaurus and go word nazi somewhere else....and take your meds.

 

[Tahoe Man]

I don't think he meant it like screw rivian they use cheap batteries, but sealed lead acid batteries in my experience are the cheapest option for a vehicle, especially evs. Every ev and hybrid I work on has either AGM or Lithium batteries as their 12v system. Lithium LiFePo batteries work the best for their size because of their energy density, but they aren't without their own issues especially when the battery sensor is part of the battery and not replaceable separately. I was told that the rivian had AGM batteries OP just showed otherwise. Had they been AGMs most of them would have been able to be recovered.
Separate from this I call BS that one is for the right side and one for the left side of the vehicle, it likely just has two in parallel for combined power. Old 911s did the same thing but it was more for weight distribution, one small 12v in the LF and one small one in the RF corner of the car.

I agree, the whole "this battery powers this and that battery powers that" seems like BS. Then I wonder way a 7000lb truck needs two smaller batteries at all....It seems like a needless added expense.

 

[Zoidz]

I agree, the whole "this battery powers this and that battery powers that" seems like BS. Then I wonder way a 7000lb truck needs two smaller batteries at all....It seems like a needless added expense.

I can't think of a technical reason to use two batteries split left and right. I'm gussing that the reason they used two batteries was a "form over function" decision. That is, they wanted to optimize the frunk space, so two thin batteries side by side was selected. It needlessly complicates things, such as the whole thing about hooking up both batteries at the exact same time. How are the 40+ controllers/computers powered up? Also split left and right? What about the primary controller and infotainment? That's not left or right.....

 

[IPTV65]

This is the answer. There are some other articles out there that address the question.

https://www.caranddriver.com/features/a38537243/electric-cars-12-volt-batteries/

We need this…. “HYUNDAI CONNECTED THE 12-VOLT SYSTEM TO THE HIGH-VOLTAGE BATTERY TO ALLOW ITS CARS TO JUMP-START THEMSELVES.” Sorry for the caps. Was a copy/paste thing.

 

[Riviot]

I'm calling BS on your "race cars." You don't even have a K&N air filter on your Rivian!

 

[Kuro-Rivian]

I'm calling BS on your "race cars." You don't even have a K&N air filter on your Rivian!

I tried to put 110 leaded into it but can't find the filler!

Right now my '69 2002 that runs on that 110 leaded lives right next door to the r1t...it's like the ultimate juxtaposition of new and old.

 

[Throwdown]

We need this…. “HYUNDAI CONNECTED THE 12-VOLT SYSTEM TO THE HIGH-VOLTAGE BATTERY TO ALLOW ITS CARS TO JUMP-START THEMSELVES.” Sorry for the caps. Was a copy/paste thing.

The 12v is connected the HV system on all EVs via the inverter that's how the 12v system charges when the car is active. I'm not sure what hyundai is doing, maybe using capacitors in the inverter?

 

[Mark_AZR1T]

Thank you! Very informative for all the reason's others have posted. I'm going to pulling the Frunk soon to map a few things underneath. Subscribed.

 

[Indy avocado]

I agree, the whole "this battery powers this and that battery powers that" seems like BS. Then I wonder way a 7000lb truck needs two smaller batteries at all....It seems like a needless added expense.

The 12V system is there to run most of the electronics, as it's a lot easier/cheaper to get 12V compatible components than 400V ones.

The batteries are there because in certain situations the high voltage pack needs to be disconnected for safety (or in the case of a battery condition/fire) and you need the 12V system still available to run the safety critical items.

 

[IPTV65]

The 12v is connected the HV system on all EVs via the inverter that's how the 12v system charges when the car is active. I'm not sure what hyundai is doing, maybe using capacitors in the inverter?

I agree but since the 12v can go dead while the HV battery still has po

The 12v is connected the HV system on all EVs via the inverter that's how the 12v system charges when the car is active. I'm not sure what hyundai is doing, maybe using capacitors in the inverter?

I don’t dispute that but seems it’s not that simple as their are cases where the HV system has power and the 12v does not. Hyundai might have a method to force the connection when the inverter is not sending power to the 12v system for whatever reason. Not sure…just a guess.

 

[Brewbud]

I don't think he meant it like screw rivian they use cheap batteries, but sealed lead acid batteries in my experience are the cheapest option for a vehicle, especially evs. Every ev and hybrid I work on has either AGM or Lithium batteries as their 12v system. Lithium LiFePo batteries work the best for their size because of their energy density, but they aren't without their own issues especially when the battery sensor is part of the battery and not replaceable separately. I was told that the rivian had AGM batteries OP just showed otherwise. Had they been AGMs most of them would have been able to be recovered.
Separate from this I call BS that one is for the right side and one for the left side of the vehicle, it likely just has two in parallel for combined power. Old 911s did the same thing but it was more for weight distribution, one small 12v in the LF and one small one in the RF corner of the car.

I believe the Rivian batteries are AGM. SLA batteries can be AGM or lead plate. They have the same basic chemistry. Both the comparable batteries the OP compared the Rivian battery to, are AGM batteries by Chrome Battery. Unfortunately, you still can't discharge real low with an AGM as they will not recover ether. I have gone through many AGMs in my Jeeps, trucks and bikes. They are better at handling vibrations and are able to mount in any direction.

As far as separating the two batteries, I agree separating the two sides of the car doesn't make sense. I can see doing that as a way to separate the the many different computers power from the power for the other accessories though. It would be similar to the separating the DC analog and DC digital grounds on a circuit board to remove electrical noise. That is a great way to remove noise from from sensitive computer and sensor circuits. This is complete speculation by me, but chasing down and eliminating noise in sensitive circuits was a substantial part of my job. They could have a different reason for separating the two but without seeing a wiring diagram for the truck that would be my best guess. They are definitely other ways to isolate noise if using a single battery too.

IMO, a LiFePO2 battery would be much better battery for our trucks. There is more useable power available as they can discharge lower and still recover. And unlike SLA batteries they have a built in battery protection circuit to prevent battery damage. They do have issues at cold weather charging unless they have built in heaters.

Damn I wish we could get a service manual with diagrams!

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