12v second battery overcharged after using ODB port battery tender?

[flaky]

I recently started following the forum method and hooked a battery tender to ODB port to trickle charge 12V battery of my Gen1 R1T. While using, I kept battery tender on 24/7 (it was plugged to a LifePo4 battery), even while driving vehicle. About a week after using it, the 12V battery failed. Mobile service came and told me the second 12v battery overcharged to 19V. He also mentioned that ODB port is not for charging.

I am trying to understand the cause. The battery tender have no capability to overcharge to 19V. so it must be due to the vehicle charging. My guess is that the ODB only connect to the primary battery. If only the primary battery is being trickled charged, vehicle computer got confused and somehow overcharged the second battery? Anyone have a theory?

Moving forward, I think the possible options are:
1. trickle charge both batteries
2. only charge while vehicle is idle/sleep
Probably only 1 is needed?

For the context, this is the 12V battery tender I was using and also this ODB port adapter.

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[zymolysis]

Frankly, I don't know how it is possible to charge a battery to 19V. I think the chemistry wouldn't allow it. Hooking up a 19V source might overcharge it, but as soon as that source is removed, the battery voltage would drop to that which the chemistry dictates. If this is a later version, which IIRC has a capacitor in place of the second battery, I could understand it... maybe.
Keeping it connected to the Battery Tender while in operation, as you said, may have caused the internal charger to overcharge it. Connecting it to a trickle charger, when not in use, will allow it to not wake up to charge, but who knows what it does during normal operation.

 

[jerseyff]

What is the reason you (and the forums?) find it necessary to be charging/maintaining the 12V system constantly? The truck maintains the 12V system from the HV...

I am 45k miles in and never had a 12V issue. Mobile service came out and replace them under the vendor battery warranty issue a couple of months ago, but I have not had any service issues.

 

[UnsungZero_OldTimeAdMan]

What is the reason you (and the forums?) find it necessary to be charging/maintaining the 12V system constantly? The truck maintains the 12V system from the HV...

I am 45k miles in and never had a 12V issue. Mobile service came out and replace them under the vendor battery warranty issue a couple of months ago, but I have not had any service issues.

Hypersensitivity to vampire drain. That is the motivation.

 

[malditofman]

I recently started following the forum method and hooked a battery tender to ODB port to trickle charge 12V battery of my Gen1 R1T. While using, I kept battery tender on 24/7 (it was plugged to a LifePo4 battery), even while driving vehicle. About a week after using it, the 12V battery failed. Mobile service came and told me the second 12v battery overcharged to 19V.

I am trying to understand the cause. The battery tender have no capability to overcharge to 19V. so it must be due to the vehicle charging. My guess is that the ODB only connect to the primary battery. If only the primary battery is being trickled charged, vehicle computer got confused and somehow overcharged the second battery? Anyone have a theory?

Moving forward, I think the possible options are:
1. trickle charge both batteries
2. only charge while vehicle is idle/sleep
Probably only 1 is needed?

For the context, this is the 12V battery tender I was using and also this ODB port adapter.

Toss the battery tender. Problem solved. Drive well.

 

[Mathme]

I'm confused as to why the OP would keep the battery tender on via the OBD port while driving the truck, as the truck will charge the 12v battery via the HV battery . That makes zero sense. This is likely what toasted that 12v battery.

Additionally, if you drive the vehicle every day, there's really no reason to charge the 12v battery via a battery tender as that work-around is primarily for when leaving the truck parked for an extended time, or if camping off-grid.

 

[UnsungZero_OldTimeAdMan]

I'm confused as to why the OP would keep the battery tender on via the OBD port while driving the truck, as the truck will charge the 12v battery via the HV battery . That makes zero sense. This is likely what toasted that 12v battery.

Additionally, if you drive the vehicle every day, there's really no reason to charge the 12v battery via a battery tender as that work-around is primarily for when leaving the truck parked for an extended time, or if camping off-grid.

The internet is an echo chamber. And tales of 12V failure and vampire drain have some people thinking it's a way bigger issue than it is. We see it in this forum over and over.

Vampire drain is cumulatively wasteful, but unless trickle charging from wind/sun it's still spending dollars on electrons. Even if recharging with wind/sun, the gear used isn't free either. It's an irrational obsession. Agree that it makes more sense for off-grid use—with intent to preserve HV pack's SOC as much as possible.

 

[Mathme]

I agree...when going on vacation and leaving the truck parked at either the airport or home, I'll lose a little less than 1% on average per day. Not enough to have to McGyver the truck and worry that much about it.

Do I wish Rivian would get it down to even less than that...yes as that is still three complete charges per year in wasted energy

 

[Sempervirens]

I think the naysayers misunderstand the reasoning: Scale.

I have a G1 R1S, and lets say I take a 2 week vacation. Parked over 14 days (70deg in garage) I lose 28% of the main battery (=70mi of range). When I get home the last thing I want to do is charge it.

You may rebut with: just keep it plugged into L2 charger etc. This still eats 28% of the battery but tops up from the grid/solar etc. At a cost of $0.45/kWh this = 36kWh or $16.38.

By using a battery tender, the car stays asleep. In my most recent travels, while on a BT I use .25kWh per day (3.5kWh over 14 days) this is an order of magnitude lower, or $1.58 in cost.

Is $16 going to break me, of course not. Is 16 x many trips over many years inefficient and a waste of energy, yes.

Note: My BT is in a garage and does NOT stay connected while driving.

 

[UnsungZero_OldTimeAdMan]

Frankly, I don't know how it is possible to charge a battery to 19V. I think the chemistry wouldn't allow it.

It's entirely possible to overcharge. When the chemistry is full up on electrons and can't take any more, that surplus force feeding... i.e. energy... has to go somewhere. Heat. Gas, i.e. chemical reaction and irreversible change to chemical composition; a "cooked" battery.

 

[mudito]

Definitely odd. I've been using my (2x) NOCO 5A chargers directly to both batteries and the NOCO will STOP charging when the voltage reading is adecuate.

Mind you, I don't have it hooked up every day, I only do a 24hr trickle charging to my 12V batteries once a while (maybe every other month) just to keep them in good health.

Also, one of my NOCO 5A chargers has being connected to my Focus RS for more than 9 months while I wait for the new engine, I measure the voltage every so often and the Focus' battery have NEVER EVER exceeded 12.9V, so I'm sure that the NOCO takes good care of my AGM batteries

 

[flaky]

Did you charge only one battery? Was it through ODB port or direct to battery terminal?

I think the naysayers misunderstand the reasoning: Scale.

I have a G1 R1S, and lets say I take a 2 week vacation. Parked over 14 days (70deg in garage) I lose 28% of the main battery (=70mi of range). When I get home the last thing I want to do is charge it.

You may rebut with: just keep it plugged into L2 charger etc. This still eats 28% of the battery but tops up from the grid/solar etc. At a cost of $0.45/kWh this = 36kWh or $16.38.

By using a battery tender, the car stays asleep. In my most recent travels, while on a BT I use .25kWh per day (3.5kWh over 14 days) this is an order of magnitude lower, or $1.58 in cost.

Is $16 going to break me, of course not. Is 16 x many trips over many years inefficient and a waste of energy, yes.

Note: My BT is in a garage and does NOT stay connected while driving.

 

[Sempervirens]

Did you charge only one battery? Was it through ODB port or direct to battery terminal?

My car has 1 battery, BT connected via ODB2. Brand is Battery Tender by deltran.

 

[flaky]

Physics does not work that way…if your battery is, say, already 15v and your charger can only supply max 14v, there is no way to “force” the electrons into the battery, no matter how powerful the charger is.

It's entirely possible to overcharge. When the chemistry is full up on electrons and can't take any more, that surplus force feeding... i.e. energy... has to go somewhere. Heat. Gas, i.e. chemical reaction and irreversible change to chemical composition; a "cooked" battery.

 

[zymolysis]

I am 45k miles in and never had a 12V issue. Mobile service came out and replace them under the vendor battery warranty issue a couple of months ago, but I have not had any service issues.

Well, that's the reason you haven't had a 12V issue - they replaced them. Many, many people have had a 12V issue - many of them where the 12V died and they couldn't operate their Rivian.

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