How to determine when to replace hybrid battery

[sudomann]

Recently bought a 2008 RX 400H AWD with 185K miles on it. I have no idea whether the hybrid battery has ever been replaced. It's my understanding that the vehicle is sometimes supposed to drive powered by the hybrid battery.

 

When driving downwards on a slope for several minutes, the battery can go from just 2 bars, to around 75%-90%. That seems absurd to me, as if the battery's charge capacity has been entirely diminished so it only stores a fraction of what it originally could. The battery also gets depleted in a similar manner. This does not surprise me, but since I'm averaging 22 mpg, I'm not inclined to get a replacement battery.

 

Oddly enough, driving around until the battery is charged up and then parking it overnight results in diminished charged by morning. For example 80% down to 20%.

I am terrified about the hybrid battery possibly failing and shutting down the vehicle while I'm driving at speed on the highway. Are these just standard symptoms when the car is at this age or should I be looking into a replacement?

 

On that note, I'm curious whether the hybrid battery in the newer models work with my old model?

[1990LS400]

5 hours ago, sudomann said:

It's my understanding that the vehicle is sometimes supposed to drive powered by the hybrid battery.

Not really unless you are driving under about 10 mph very gently.  Even then, range in EV mode is very low.

Does the internal combustion engine shut down at least some of the time when you are stopped at a traffic light?  If it does then the traction battery is functioning to some extent.

If you are doing a lot of highway driving, you might be noticing that the hybrid version of the RX doesn't get much better gas mileage than the regular RX.

From the 2008 RX and RX hybrid sales brochures:

RX:Fuel Consumption 18/23 mpg (FWD)19
(estimated city/highway) 17/22 mpg (AWD)19

RX Hybrid: Fuel Consumption 27/24 mpg (FWD)
(EPA estimated city/highway) 26/24 mpg (AWD)

EPA fuel consumption estimates are widely seen as fantasy.  We've rarely achieve EPA estimates on our vehicles.  For example, my wife's 2012 Prius v hybrid - owned since new - has been averaging only 32 mpg in mostly city (35 mph to 45 mph) driving.  It's EPA city/highway estimates are 44/40 mpg.  Of course, the battery in her Prius is over 7 years old and might be getting weak although the car has only 43,000 miles on it.  Her low city fuel economy could be related to her rarely driving more than 15 miles/day and there aren't many traffic lights or downhill slopes that would trigger regenerative braking on the routes she takes.  Traction battery charging is totally dependent on regenerative braking.

I have to assume that a Lexus dealership could test your traction battery and the regenerative system for health.  

If your traction battery is weak and you want to replace it, there are several companies that sell re-manufactured ones ... like:  https://greenbeanbattery.com/lexus-rx400h-hybrid-battery-replacement/

A traction battery supplier like Green Bean Battery should be able to tell you if traction batteries for new model years can be used in your RX.

 

[sudomann]

53 minutes ago, 1990LS400 said:

Does the internal combustion engine shut down at least some of the time when you are stopped at a traffic light?  If it does then the traction battery is functioning to some extent.

When the wait is long enough, it does. Or when I start the car in the parking lot, but don't drive off immediately.

I've noticed the traction battery briefly kick in from time to time while driving; Assuming I am right when assuming moving arrows from the battery towards the wheels on the energy monitor means the traction battery is helping...

[1990LS400]

8 minutes ago, sudomann said:

When the wait is long enough, it does. Or when I start the car in the parking lot, but don't drive off immediately.

I've noticed the traction battery briefly kick in from time to time while driving; Assuming I am right when assuming moving arrows from the battery towards the wheels on the energy monitor means the traction battery is helping...

Those are all signs that the traction battery is functioning.

Funny, I've looked at the energy monitor screen on my wife's Prius only a couple of times in 7 years although I don't drive the car much - mainly to the gas station and car wash.  I'm sure that my wife has never looked at it.  We didn't buy the Prius because it was a hybrid or due to its fuel economy - only because it was a fairly small wagon-like vehicle that my wife was comfortable driving and it had must-have safety features like automatic emergency braking (Pre-Collision System).

We'll likely buy the 2021 Toyota RAV4 plug-in hybrid that was announced last week to replace her Prius when it becomes available.  It's suppose to have a 20 to 25 mile range in EV mode.  Since she averages only 7.6 miles of driving per day to get to and from Yoga class, I might be refueling a RAV4 plug-in hybrid only once a year.  On average, I refuel the Prius about every 6 weeks.