Third day with new car, dead 12V battery, second day in a row :(

This seems to be affecting some RX350h/RX500h and RX450h+ too. Either a bad batch of batteries or the many connectivity features of the car (it connects to the network a lot. eg. Drive Pulse) drains the 12V battery. However, it does not affect everyone. If a bad batch, change battery at dealership.

 

The passive load on the battery has been increasing in all cars through the years from the increase in features. Then full hybrids tend to have smaller batteries. Some have reported Toyota hybrids with dying 12V issues in the past.

Then bad batteries are a thing, which this could be.

You should have no issues with how you plan to use the car.

 

I haven't had the issue yet as a mostly daily charger. So it seems to be hit or miss, honestly

 

I bought an "ANCEL BM200 12V Car Battery Tester" off Amazon for $26 and here's a chart of the last 3 days and some shocking findings. Overall the car seems to be doing an adequate job of keeping the battery charged but the exact algorithm is quite unexpected. Normally I would expect that when you drive a car it will be good for the 12V battery and charge it to 100%. What we've been theorizing is that letting the car sit on the charger overnight is draining the battery. We've also read that the 12V battery is always charged when plugged in and the traction battery is being charged. ALL WRONG!!!

What I found is that the worst thing you can do for your battery is actually drive the car, and the only surefire way to charge the 12v is to put it into Ready mode but not drive the car. Charging the traction battery does not ALWAYS charge the 12V battery - it does it sometimes but sometimes it decided you don't need it. I also put the car manually into HV mode and not even that charged the battery. Surprisingly I found no voltage drop at all overnight sitting on the charger fully charged.

In the graph all the big dips are when the car is being driven. The only spikes to 100% are when I manually put the car into ready mode and let it charge. The flat lines are sitting on the charger. Surprisingly it burnt 5% of my PHEV charge in READY to boost the 12v from 85% to 100% and perhaps that's why it doesn't always charge the 12V while driving. The car does charge the battery when it's good and ready - it lets it get down to about 60% which is in the low 12 V range. So your battery shouldn't ever drop below 12V. But if you're watching the battery it's true "voltage anxiety" as it drops and drops and drops before it decides it wants to charge the battery. When it does charge it, it only charges it to about 85%. I'm not an expert but wouldn't it be better for a 12V to always be charged to 100% while driving and while plugged in? I think that for lithium batteries, a charge cycle between 60-85% sounds perfect. But is this the right thing for standard 12V flooded lead acid which have always been designed to be kept as close to 12V as possible? It almost makes we wonder if the software folks were told it was going to be LiFePO4 but the hardware guys had their own ideas.

This is only after 3 days and I didn't spend a ton of time to log every single action so let the criticism begin, but I hope that others will buy this monitor and try it as well. Those who are finding the battery dying while on the charger should be looking for vampire power drains (some have suggested LoJack but my Toyota dealer put in a battery powered disposable tracking device, not wired). I will continue to monitor this and perhaps my theory will change with more data but I wanted to share this preliminary surprise.

 

@vermouth and others, my findings in Europe PP base model are the same. No charging unless you are in Ready BUT remain in P. Then voltage rise till 14,6V. Battery reaches 100% in half an hour. Normally sits at 60%. Same as your findings. Doesn't charge if you are only stumping on the brake pedal. See 5 days data.

 

I have further surprising findings. It appears that just leaving a USB-C cord without anything attached plugged into the front outlet labeled with the charging symbol will drain the car's battery. It appears to keep the car's computer awake even though it's not powered on. I noticed that after I left an item connected overnight and noticed a continual drain so I disconnected the item and the drain continued until I removed the cord from the outlet. This seems baffling but some USB-C cords have chips in them. Page 458 of the manual actually may hint at this problem "To prevent 12-volt battery discharge Do not use the USB Type-C charging ports for a long period of time when the hybrid system is off".

 

I have my dash cam plugged into one of the rear USB C ports via a USB C to USB A dongle. So what you saying is that because the dash cam is plugged in on the other end there is no drain issue? To be clear I have not had any 12V issues (yet) and have run the dash cam setup like this for the last 7 months.

 

Having an actual device connected doesn't help - that was how I detected the initial drain. But clearly it's not happening to you. I suspect that your USB-C to USB-A dongle may be saving the day because it eliminates any USB-C circuitry or perhaps the rear ports are different. I'll have to try a dongle as an experiment.

 

From a thread on a different topic, it sounds like the rear USB ports are power only. With no data transfer, there wouldn't be a reason for a computer to stay awake.

 

What kinds of USB-C cables can theoretically cause this behavior? Aren’t the majority of USB-C cables passive and without any active chip (only talking about cables, not USB-C connected receptacles/devices). I’ve heard of active Thunderbolt (USB4) cables that use a USB-C connector, but that isn’t generally what one would use to connect devices in a car.

Is anyone else noticing or able to replicate this behavior with cables keeping the car awake?

I don’t have a controlled way of testing it myself at the moment.

 

Mine has two USB-C ports in the front. One is data transfer and the other is power only.

 

Don’t forget the power-only ones in the center console storage – those are the only ones I use most of the time.

 

That is a Thunderbolt 4 cable used to connect monitors, Thunderbolt hubs, and external drive enclosures. I have one plugged into a LG 5K monitor into a Mac Mini. You won’t find these in cars plugged into phones, since the only reason people have them is to plug into high bandwidth devices (for example: connecting a MacBook to a 4K monitor with a USB hub while providing power).

An Apple USB-C to USB-C cable won’t be designed the same way as this Thunderbolt cable. However, Thunderbolt 3/4 (sometimes conflated with USB4) cables do use a USB-C connector, which leads to a bit of confusion, since a Thunderbolt cable is superficially similar to a USB3 cable with a USB-C connector. That article is misleading, since a common USB-C charging cable (with USB2 data rates) from Apple actually costs $19-29 240W USB-C Charge Cable (2 m) - Apple

You probably don’t have one of these Thunderbolt cables in your car, right? The one that comes with your phone is probably the cheap USB-C connector without a chip in it.

 

Seems you're kind of just guessing right now. You want a multimeter plugged inline on the positive side of the 12v. Then get the display in a position where you can read it without having any doors open. Cars take a while to idle down. My 08 took about 15-30 minutes to hit true idle.

So with nothing else plugged in, no usb, no obd2, no dash cam, nothing, you find your baseline idle power draw. Also consider keeping the keyfob away from the car when you go to check the multimeter. In fact you may want to turn off the keyfob (

), and make sure not to have it with you when you go to check the multimeter so you don't wake the car.

Check on the car about every 15 minutes after locking it and having the multimeter set up. Note the time and amperage draw. DO NOT OPEN THE DOORS OR WAKE THE VEHICLE IN ANY WAY. Do not use the Toyota app. Do not trigger the car's computer to wake up.

Now you have a baseline. If that amperage draw is already high without anything else going on then your issue lies beyond your usb/obd2/keyfob, etc (at this point I'd be pulling fuses for non-critical components, DCM, poutlet, obd2, etc and then monitoring my idle draw again over time). If it's low and the car is properly sleeping now you can add a variable. Plug in a bunch of USB cables for example. Lock the car and make sure the multimeter is visible. Same monitoring.

There's no need to be guessing at stuff like it seems you are. Just use a multimeter.

 

I mean you're saying it's USB cables and if it were I feel like this issue of a parasitic drain would be more widespread since pretty much the vast majority of us leave cables plugged in.

So, if you want to be certain before making definitive claims, especially claims that defy expected outcomes, follow what I suggested. It'll be good for you as well to be able to track and monitor your own parasitic drain issue. Also I did make a mistake in my info, you can put it inline with positive or negative. Negative might be less complex to go inline with since there's less connected to it.

If you don't already own a multimeter, spend a few extra $ and get a clamp one. It'll still have the physical probes but oh my god having a clamp multimeter can make some issues way easier to track down. Worth it.

 

Are you asking that the multimeter be plugs in-line (in series) with the plus or minus terminal wiring on the battery ?
So you want to use the amp meter feature of the multi-meter ?
The multimeter I have (Fluke 77 IV) only has two amp ramges, 400 MA and 8 A. These are fuse protected circuits, if the amp rating of the circuit is exceeded the fuse blows.
Any mistake while attaching the MM circuit to the battery, key fob too close by, doors locked/unlocked (Horn and lights flash) putting the vehicle in READY state, is likely to exceed the rating of these circuits, especially if using the 400 MA circuit to find parasitic loads. This is not a good idea.
Using a cheap clamp on ammeter circuit to measuer small DC currents is not usually accurate readings or consistent readings.
You should always personally try the metering setup you recommed to others, so you have a valid suggestion.