Anyone Test 12-volt Charging with Volt Meter?

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Jan 31, 2024 | 03:09 PM

NX450Guy

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From: Oregon

Anyone Test 12-volt Charging with Volt Meter?

Has anyone taken a volt meter to test the 12 volt battery to see if actually charged while the engine sat on “Ready?” Did it look to be charging while on “Ready” in both EV mode and HV/AUTO modes? Since I’m a low mileage NX 450 driver who has already had two dead batteries, I’m trying to leave it parked on Ready mode to charge up. Some dealerships say you have to turn the wheels (drive) to charge the 12-volt. Before I buy a volt meter, wanted to see if anyone already tested 12 volt charging while engine sat in “Ready” mode. I seem to mostly gripe on here, but other than the 12-volt issue, I love the NX! (I know, some will say: “Other than that issue Mrs. Lincoln, how was the play?”&#128514

Jan 31, 2024 | 04:36 PM

Aegean

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On my ES 300h, when off battery is around 12.4 but when I put in.ready (in park) I get 14.2v so the DC to DC converter provides power. I have tested with voltmeter. A typical car alternator would depend on engine rpm and preferably perform better with driving but on a hybrid the DC power comes from the DC to DC converter originating in HV battery. The engine rpm or if it is on or off is irrelevant.

Jan 31, 2024 | 04:58 PM

NX450Guy

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From: Oregon

Quote:

Originally Posted by Aegean

Thanks for the info. Do you know logically if it matters whether it is in “ready“ on EV or HV/Auto mode on the plug in hybrid? 12 volt charges just the same?

Jan 31, 2024 | 05:08 PM

gamma742

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From: San Diego

Makes no difference, 12v charges just the same.

Jan 31, 2024 | 05:14 PM

NX450Guy

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From: Oregon

Quote:

Originally Posted by gamma742

Makes no difference, 12v charges just the same.

Excellent, thanks, wish the dealers could be so definitive.

One last Hail Mary question: Do you know approximately how long the NX needs to sit on ready mode to be fairly sure the 12 volt charge is full?

Jan 31, 2024 | 05:37 PM

gamma742

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That, I don't know but I do short 5 mile trips in EV mode and when I plug in the 12v battery tender, it's flashing Green and within 2-4 minute it's Solid Green meaning it's full charge.

on a side note. Plugging in the HV Charger and waiting on the schedule to kick in at midnight for the cheaper electric rates, I found the 12v also charging 5 minutes when from flashing Green to Red for about 20 minutes so having the HV Charger plugged in gets the vehicle computer thinking and using 12v.

I think (hope) Toyota/Lexus should come out with a software update for the 450h+ to correct some of the parasitic draws on this vehicle. Too many people have complained of coming out to a dead 12v system requiring a jump or a new battery. I have been told by a Lexus Technology Expert never to use ACC Mode. Keep the car in Ready for making any personal setting changes or listening to music.

Jan 31, 2024 | 06:28 PM

Aegean

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From: VA

Quote:

Originally Posted by NX450Guy

The usable output of the DC to DC converter that goes to 12v battery on my 300h is about 70 amps initially. As the 12v battery charges it draws lower amps. The 12v battery is 57 AH so from empty to full it could be less than an hour if 70 amps were steady. In reality, I think it is more like 2 hours to fully charge.

I do not recommend to have the car in ready mode for 2 hours because the HV battery will suffer with the engine turn on several times and the charging/discharging. I would take a long drive instead or buy an inexpensive battery smart charger for AGM batteries.

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Feb 1, 2024 | 06:42 AM

Droid13

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From: Toronto, ON

Quote:

Originally Posted by Aegean

I do not recommend to have the car in ready mode for 2 hours because the HV battery will suffer with the engine turn on several times and the charging/discharging. I would take a long drive instead or buy an inexpensive battery smart charger for AGM batteries.

I don't think its possible to let it sit for 2 hrs in ready mode anyway unless you stay in the car to override. At 1hr sitting with no driver actions, it will shut off on its own. A fix from the earlier hybrid days when people would often forget to shut off their cars. I did this once in the early owner days of my 2007 Camry Hybrid, and also came back from a tire swap on that car to see the car left on in the parking lot. Early days of hybrids plus early days of push button start made for some relearning but I guess ToyLex made these changes to make sure no one poisons their garage if accidentally left running overnight.

Feb 1, 2024 | 10:30 AM

#10

StefanoS

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From: CA

Quote:

Originally Posted by Aegean

Here's what I have placed in both my RX450h+ and my wife's NX450h+. These were cheapies and I ordered two of them from Amazon. Although the LED display is not clear in this photo, it reads 14.1v in EV mode. The readout will fluctuate, as I tend to keep my eye on it while driving. It can be anywhere from 12.2v, up to 14.2v. While I am not certain how accurate they are, at least it shows that there is some charging going on. I also attached a harness for my NOCO trickle charger for charging, should the battery require a bit extra juice. I also carry a NOCO Boost XL GB50 in each vehicle, just in case. Here's a link to the voltmeter

Amazon

Last edited by StefanoS; Feb 2, 2024 at 11:58 AM.

Feb 2, 2024 | 11:09 AM

#11

TheCDN

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From: Niagara Falls, Ontario

I just bought this item from Amazon for my '22 NX 350h and can confirm that it's accurate for what is at the 12 volt battery posts when confirmed with a good voltmeter. Very quick and easy way to see when the 12 volt is being charged as in accessory mode or ignition on, it surges up to about 14.5 volts when the 12 volt is getting charged by system. My battery is on it's way out like so many others have experienced and when nothing is running at all and only on accessory it's dropping down to 11.7 11.9 volts which is BAD. Using a 2 amp NOCO trickle charger and carry a NOCO GBX45 for any needed boost for now. Dealer will be doing a load test next appointment and hopefully declaring it's dead on arrival and hopefully replacing it with something more robust.

https://a.co/d/0SrauM2

Can I ask the group are your replacement batteries from dealer getting 'upsized' to a higher cold cranking amp rating or switching to an AGM type battery?

LSFT had his battery replaced on his '22 450h with a 600 CCA battery which is quite a jump in size.

Last edited by TheCDN; Feb 2, 2024 at 11:16 AM.

Feb 2, 2024 | 11:57 AM

#12

StefanoS

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From: CA

If my 12v croaks prior to the warranty expiration, I may let the Lexus dealer replace it but, if I have to foot the bill after the warranty, I would probably opt for an Odyssey ODP-AGM47H5L2.