When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
I’ve been seeing some posts about the 12V battery staying charged. Hoping that doesn’t pertain to the hybrid model.
I have been looking at the online user manual, but have yet to see how I can force the engine to run while I’m sitting in my driveway trying to figure out how do use all these new features. TIA
I’ve been seeing some posts about the 12V battery staying charged. Hoping that doesn’t pertain to the hybrid model.
I have been looking at the online user manual, but have yet to see how I can force the engine to run while I’m sitting in my driveway trying to figure out how do use all these new features. TIA
As long as the car is in ready mode the 12V battery will not drain.
When I first received my 2025 PHEV - I spent better than an hour in my garage "messing" with the various settings, adjusting this and that or trying this and that, car in the ACC position HVAC off - and contrary to the warnings on this forum, the 12v battery did not die. My PHEV has a battery charge setting button on the console. When I push the button in the "ready " mode, the engine starts, and runs while sitting in park. I've never run it more than 10-15 minutes, so I don't know how long it runs. The owners manual says it will charge the traction battery to 80%, but no reference to the 12v system. FWIW
I’ve been seeing some posts about the 12V battery staying charged. Hoping that doesn’t pertain to the hybrid model.
I have been looking at the online user manual, but have yet to see how I can force the engine to run while I’m sitting in my driveway trying to figure out how do use all these new features. TIA
You absolutely don't need to run engine to charge 12V battery in hybrid. Once you press Start button (or do remote start) and start "hybrid system", it starts charging.
You can check the voltage in the lighter outlet or anywhere else using $20 tester. It varies from 13.6V to 14.4V depending on load at the moment. E.g. it may be 14.4V in Park or with DRL lights off. Or 13.6V in Drive with lights and A/C on. 13.6V is enough to charge the battery. Like historically German cars had only 13.8V at regulator, Japanese over 14V. Either is fine if it isn't a classic car that drops voltage on oxidized connectors. If it's old, check voltage on the battery terminals directly. As once you stop charging, fully charged battery has around 12.6 V only.
ACC (accessory) mode is disabled by default in newer NX 350h. You can still enable it in settings, but then you really risk ruining your 12V battery. Lead-acid batteries can't stand full discharge, and cars don't do good management to prevent it like they do with traction battery. Regular starter batteries can't stand even half deep discharge.
If your 12V battery reads like 12.2V after staying in car overnight, or you get dozens of random error codes, then you should get concerned. It means it is already ruined and can't hold charge. Or you left car for a month without trickle charger. Or you have parasitic load. Like random third-party chinesium gadget that drains electricity. E.g. some third party cameras are smart enough to disconnect when voltage drops, but 12V battery will be already half empty once it happens and will be ruined prematurely over time.
If you want to hunt for parasitic load, you need to get automotive clamp ampermeter that allows to measure current without cutting the wire. They are cheap for low quality ones. Or just go to an auto electric professional.
When I first received my 2025 PHEV - I spent better than an hour in my garage "messing" with the various settings, adjusting this and that or trying this and that, car in the ACC position HVAC off - and contrary to the warnings on this forum, the 12v battery did not die. My PHEV has a battery charge setting button on the console. When I push the button in the "ready " mode, the engine starts, and runs while sitting in park. I've never run it more than 10-15 minutes, so I don't know how long it runs. The owners manual says it will charge the traction battery to 80%, but no reference to the 12v system. FWIW
That charge mode is used to charge the traction battery and not the 12V battery. There is no button to charge the 12V battery. Keeping it in Ready mode, idle will allow the DC to DC Convertor to charge the 12V battery.
Here's some proof that at least with my '22 NX350h, that the design of the 12 volt infrastructure does not prioritize recharging the 12 volt battery. In February 2024 I had my original battery replaced by dealer with a new AGM 600 CCA battery under warranty as original was not holding a charge.
Today is Saturday August 24, I took these images from a 12 volt monitor I have installed on my car, along with a trickle charger just after having the battery replaced.
On Thursday 22nd in morning I disconnected my trickle charger as we were going to head out on a 46 mile highway trip and returning in the evening same day. I put the trickle charger back on in late evening of 22nd. I removed the trickle charger on the 23rd to run some short errands around town. As of Sat Aug 24 when these images from my monitor were taken I hadn't put the trickle charger back on.
The Red coloured arrows indicate when trickle charger was on the battery, all other times I was either travelling in car or it was sitting in my garage turned off. You will see the 46 mile trip which took about 50 minutes of highway driving and a small amount of stop and go traffic failed to bring my 12 volt's state of charge up to any significant increase.
The double sided arrows on the State Of Charge graph are when the Trickle Charger had been applied to battery raising the SOC to 100%.
The double sided arrows on the Voltage graph are when I was driving the car. Note that the 12 volt battery did not receive any significant lasting improvements to the measured Voltage at the battery immediately following the completion of my road trips from the cars onboard management of the 12 volt battery. It began to drop in voltage as soon as the car was shut off. So there's definitely parasitic draw prevalent in the car such that it's pulling down a massive 600 CCA battery immediately.
Now I will concede this battery monitor could not be tested and proven that voltage was 100% accurate in it's readings, but I do also have a plug in voltmeter in my accessory plug in bin under the wireless charger that seems to corroborate with similar readings. The SOC seems to align also with my trickle charger which eventually shows a solid green light when it's brought battery up to 100%, then from there it will begin 'topping up' as needed and pulse red.
Here's some proof that at least with my '22 NX350h, that the design of the 12 volt infrastructure does not prioritize recharging the 12 volt battery. In February 2024 I had my original battery replaced by dealer with a new AGM 600 CCA battery under warranty as original was not holding a charge.
Interesting. Did you measure voltage when shifted into Drive or driving? It's not obvious on the multi-day graph scale.
Did you or dealer measure amperage when the car is shut off? It looks like it's dropping charge too fast, either because of high (parasitic) load, or the battery has reduced capacity.
It should be the Lexus responsibility to fix the parasitic load if you don't have extra devices connected.
Here's some proof that at least with my '22 NX350h, that the design of the 12 volt infrastructure does not prioritize recharging the 12 volt battery. In February 2024 I had my original battery replaced by dealer with a new AGM 600 CCA battery under warranty as original was not holding a charge.
Thanks for the data. There's data also in the RX forum from myself and others, mostly from the RX450H+, although this maybe the first time anyone shared very similar data from a 350H. I suspect Lexus may have taken the Rav4 (Prime's) 12 V charging subsystem and copied/pasted it to the NX and RX lines - resulting in this problem because the NX and RX have way more sensors and electronics, "illuminated door sills" and probably also parasitic drain at least in some cars.
Question: Which specific AGM battery did your dealer replace with ? In the US, dealers are refusing to replace with AGM batteries, based on feedback in the RX forum by people's interaction with dealers. I'm curious what the Ampere-Hour rating of your dealer-provided AGM battery is ? Can you please share ? For this particular problem, its the Ampere-Hour rating (for reserve capacity) that is likely to matter in preventing sudden battery death, rather than the Cold-Cranking Amps, since there is no starter motor or starting problems, and instead loss of charge (A-h).
Thanks for the data. There's data also in the RX forum from myself and others, mostly from the RX450H+, although this maybe the first time anyone shared very similar data from a 350H. I suspect Lexus may have taken the Rav4 (Prime's) 12 V charging subsystem and copied/pasted it to the NX and RX lines - resulting in this problem because the NX and RX have way more sensors and electronics, "illuminated door sills" and probably also parasitic drain at least in some cars.
Question: Which specific AGM battery did your dealer replace with ? In the US, dealers are refusing to replace with AGM batteries, based on feedback in the RX forum by people's interaction with dealers. I'm curious what the Ampere-Hour rating of your dealer-provided AGM battery is ? Can you please share ? For this particular problem, its the Ampere-Hour rating (for reserve capacity) that is likely to matter in preventing sudden battery death, rather than the Cold-Cranking Amps, since there is no starter motor or starting problems, and instead loss of charge (A-h).
Since the12v battery is not used to crank the engine when starting, then maybe a deep cycle marine battery is best.
Here's some proof that at least with my '22 NX350h, that the design of the 12 volt infrastructure does not prioritize recharging the 12 volt battery. In February 2024 I had my original battery replaced by dealer with a new AGM 600 CCA battery under warranty as original was not holding a charge.
Today is Saturday August 24, I took these images from a 12 volt monitor I have installed on my car, along with a trickle charger just after having the battery replaced.
On Thursday 22nd in morning I disconnected my trickle charger as we were going to head out on a 46 mile highway trip and returning in the evening same day. I put the trickle charger back on in late evening of 22nd. I removed the trickle charger on the 23rd to run some short errands around town. As of Sat Aug 24 when these images from my monitor were taken I hadn't put the trickle charger back on.
The Red coloured arrows indicate when trickle charger was on the battery, all other times I was either travelling in car or it was sitting in my garage turned off. You will see the 46 mile trip which took about 50 minutes of highway driving and a small amount of stop and go traffic failed to bring my 12 volt's state of charge up to any significant increase.
The double sided arrows on the State Of Charge graph are when the Trickle Charger had been applied to battery raising the SOC to 100%.
The double sided arrows on the Voltage graph are when I was driving the car. Note that the 12 volt battery did not receive any significant lasting improvements to the measured Voltage at the battery immediately following the completion of my road trips from the cars onboard management of the 12 volt battery. It began to drop in voltage as soon as the car was shut off. So there's definitely parasitic draw prevalent in the car such that it's pulling down a massive 600 CCA battery immediately.
Now I will concede this battery monitor could not be tested and proven that voltage was 100% accurate in it's readings, but I do also have a plug in voltmeter in my accessory plug in bin under the wireless charger that seems to corroborate with similar readings. The SOC seems to align also with my trickle charger which eventually shows a solid green light when it's brought battery up to 100%, then from there it will begin 'topping up' as needed and pulse red.
This is exactly the same observations I made and that is why I advised to let the car idle to allow it to charge the 12V battery. I took like 2 hrs drive and it only charged the 12V battery 2%. It's not like it's not charging the 12V battery, but a very nominal charge. it keeps the 12V battery at 12.8V which does provide a little charge, but not enough to keep it charged. One thing I observed is that you need to wait about 30 mins to allow the voltage to stablize to get the correct reading and that is why the charts show a drop immediately after you power off. Keep in mind when you power off the car, the headlights are still on for a short time and then seats would move (if you turned it on), the mirrors fold.
I believe in my video, I showed that after the car running for 1 hr it auto power off, but the headlights do not power off and the state of charge can drop from 100% to 60% in no time.
Thanks for the data. There's data also in the RX forum from myself and others, mostly from the RX450H+, although this maybe the first time anyone shared very similar data from a 350H. I suspect Lexus may have taken the Rav4 (Prime's) 12 V charging subsystem and copied/pasted it to the NX and RX lines - resulting in this problem because the NX and RX have way more sensors and electronics, "illuminated door sills" and probably also parasitic drain at least in some cars.
Question: Which specific AGM battery did your dealer replace with ? In the US, dealers are refusing to replace with AGM batteries, based on feedback in the RX forum by people's interaction with dealers. I'm curious what the Ampere-Hour rating of your dealer-provided AGM battery is ? Can you please share ? For this particular problem, its the Ampere-Hour rating (for reserve capacity) that is likely to matter in preventing sudden battery death, rather than the Cold-Cranking Amps, since there is no starter motor or starting problems, and instead loss of charge (A-h).
Dealer confirmed it was an AGM 600 CCA 'Lexus' Battery part number COPBS-8497R I don't see an Amp HR rating on exterior
LSFT - Yes I have a little plug in 12 Volt meter that I keep plugged in just under wireless charging tray too, I've observed similar readouts that have it up to 13.8 - 14.0 volts for first 1/2 hr or so and then it settles down to 12.8 - 13.0 volts providing not much to recharge 12 volt battery. As this reading is at the 12 volt adapter I'm not certain the DC to DC unit is just simply responding to immediate 'draw' on 12 volt system only and providing just what's needed to run anything asking for 12 volts. You see the 12 volt battery won't 'ask' to be charged it will simply continue to deplete over time. Somehow the system needs to push amperage back into the battery to make it recharge just like it does for traction battery. I feel this is the flaw in the design, it doesn't prioritize recharging the 12 volt it simply provides enough 12 volt to 'keep the lights on' only.
I make a habit of rotating the headlight switch off all the way then back to auto setting every time I get out of car so I force the headlights to shut off right away and not time out. I lock up the car with the door handle button and walk away and place the fob into a faraday pouch as well. So as quick as I can I 'shut down' the car right away and not have it 'looking' for my keyfob. When I wash car for example I unlock it and then put keyfob into faraday pouch as well, so I'm able to open and close doors if needed but again, don't have car awakening by fob thinking I'm gonna step in and drive it.
As I have a 350h I'm not certain putting the car into Ready will induce the car to recharge the 12 volt at that point. I will test this out soon though to see how my 350h handles Ready mode with the 12 volt battery.
08-22-24, 08:17 PM
12V Battery
