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mpg decrease when charging the HV battery while driving

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Old Mar 17, 2025 | 09:54 AM
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Question mpg decrease when charging the HV battery while driving

Hi all,
We're taking our first road trip next week and may not be able to recharge the HV battery enroute for 2 weeks. I have read that there is a mode to charge the battery from the engine while driving but I"m wondering how much this decreases your mpg. We'd be doing this at freeway speeds (~72mph). Thanks in advance for your replies.
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Old Mar 17, 2025 | 04:51 PM
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Originally Posted by kindofblue
Hi all,
We're taking our first road trip next week and may not be able to recharge the HV battery enroute for 2 weeks. I have read that there is a mode to charge the battery from the engine while driving but I"m wondering how much this decreases your mpg. We'd be doing this at freeway speeds (~72mph). Thanks in advance for your replies.

It's charge mode to charge the battery while driving on the freeway

I've don't some testing with charge mode in my 12 month ownership video.

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Old Mar 18, 2025 | 09:12 AM
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Originally Posted by kindofblue
We're taking our first road trip next week and may not be able to recharge the HV battery enroute for 2 weeks. I have read that there is a mode to charge the battery from the engine while driving but I"m wondering how much this decreases your mpg.(~72mph).
From my daughter who drives her 2025 NX450h+ weekly to/from Ithaca & Philadelphia: in city driving, she turns the charging on because it can make use of the braking energy (which would be otherwise wasted) to charge the battery. On freeway, she turns it off because there is no braking. The energy to charge the battery is taken from the gasoline engine thus mileage will suffer. She didn't say how much 'suffering' it was.
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Old Mar 18, 2025 | 11:17 AM
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Originally Posted by pentaprism
From my daughter who drives her 2025 NX450h+ weekly to/from Ithaca & Philadelphia: in city driving, she turns the charging on because it can make use of the braking energy (which would be otherwise wasted) to charge the battery. On freeway, she turns it off because there is no braking. The energy to charge the battery is taken from the gasoline engine thus mileage will suffer. She didn't say how much 'suffering' it was.
Um... that's not how that works. Braking energy will always go to the battery unless she's hard on the brakes - even then a portion goes to the battery and the rest to the mechanical brakes.
The other case is if she's in Neutral. I believe neutral forces the use of mechanical brakes - or at least it does on the Prius and I'm assuming Toyota/Lexus didn't reinvent that wheel for the NX specifically
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Old Mar 18, 2025 | 12:49 PM
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Originally Posted by Thuwaragan
Um... that's not how that works. Braking energy will always go to the battery
I agree, the vehicle will try to recover braking energy whenever it can, regardless of mode of operation. I think the logic expressed by "the daughter" is backwards. The main reason for force charging the hybrid battery while driving is to utilize engine power during times when the engine is operating at its most efficient times, so that at a later time the battery can be used during times when the engine would not be efficient. Driving on the highway is a good time to force charge because at highway speeds the engine is operating far more efficiently than it does in the city. The hit to mpg would IMO be lowest. When driving in the city, I'd think turning on the charge up feature would be a mistake, the engine is not efficient, and mpg would suffer more.
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Old Mar 18, 2025 | 02:55 PM
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Thanks all.

I'm wondering how to get the most efficient energy use on this trip. Would I be correct in using the battery until it switches over to the engine then having the engine recharge the battery? This assumes a relatively flat, constant 72mph on the freeway. It's doubtful we'll be able to recharge on L2 or 110 during the 2k trip.
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Old Mar 18, 2025 | 07:00 PM
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I would use HV mode when driving on the freeway. Use EV when driving on local roads.
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Old Mar 20, 2025 | 10:27 AM
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I would follow LSFT's lead here. Watch his in depth videos explaining all things 'NX' !

It's my understanding that with either the 350h hybrid or 450h+ you really don't have any control over the regenerative braking system. I've been travelling on the highway in my 350h and let off the gas peddle only and the car will grab the energy from decelerating the car. Take some time and put up the energy flow picto gram on your centre stack screen you will see when the wheels are feeding energy (blue colour for electrical energy flow) into the system. It happens all the time, not just when braking. And I don't think you can reduce or prevent that at all. Why would they design a high mileage car only to not take advantage of the energy recovery process from the wheels / brakes. You will only be able to prioritize the 'use' of your high voltage traction battery with your selections of HV or EV.

But please be safe and cautious and fill up your gas tank always before a long trip! Plan for the best, prepare for the worst. This is the best feature you have with an HEV or PHEV!
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Old Mar 20, 2025 | 01:21 PM
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Originally Posted by TheCDN
I would follow LSFT's lead here. Watch his in depth videos explaining all things 'NX' !

It's my understanding that with either the 350h hybrid or 450h+ you really don't have any control over the regenerative braking system. I've been travelling on the highway in my 350h and let off the gas peddle only and the car will grab the energy from decelerating the car. Take some time and put up the energy flow picto gram on your centre stack screen you will see when the wheels are feeding energy (blue colour for electrical energy flow) into the system. It happens all the time, not just when braking. And I don't think you can reduce or prevent that at all. Why would they design a high mileage car only to not take advantage of the energy recovery process from the wheels / brakes. You will only be able to prioritize the 'use' of your high voltage traction battery with your selections of HV or EV.

But please be safe and cautious and fill up your gas tank always before a long trip! Plan for the best, prepare for the worst. This is the best feature you have with an HEV or PHEV!
Thanks. I'm realizing that. I noticed today that applying pressure to the brake the driver's display shows "charging."
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Old Mar 20, 2025 | 02:55 PM
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If you're in ECO or Normal mode, the driver's display will show you Charge/Eco/Power bands in the center dial.
The harder you step on the breaks, the deeper into the "charge" section the blue bar will go. Once you fill up the charge section then the remaining braking force is applied by the friction brakes. So if you're trying to get as much power back into the battery (and granted this is a tiny amount), try to plan ahead and brake earlier so you're not going beyond the max of that section.
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Old Mar 21, 2025 | 06:10 AM
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I had the same question after I bought my PHEV, and figured out you gotta be a lot smarter then me to quantify it. Now I just drive it, let the car decide. The EV only mileage varies. The ICE mileage varies and can't be isolated from the total miles. Regenerative braking affecst the EV mileage etc etc. I'm sure itr has some effect, but it can't be enough to worry about or spend time trying to manage.
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