While on our first road trip in our 2023 XLE hybrid with the NiMH battery, we've encountered several instances of the limitations of the hybrid system in recovering energy in mountainous terrain. Our experience wasn't something I read about in scouring this forum, and while it would have been a factor in the purchase decision, I think it's pretty likely we would have ended up with a Rav4 hybrid anyway. My wife and I are both very satisfied with the performance, comfort, and efficiency of our Rav. I want to leave this here so other potential owners can be fully informed.
When descending an extended and steep downhill of three or more miles, the hybrid battery will become fully charged and at that time, a few things will happen.
First, the Rav becomes unable to operate in EV mode. The EV mode light turns off, and pressing the EV button generates a message that EV mode is unavailable.
Second, the ICE engine spins up. I'm not sure if there is fuel going to the engine or if it is just being spun up to provide additional drag with fuel flow shut off. When this happens and the engine is not at full operating temperature, the engine coolant gauge will show the engine continues to get warmer. I had one instance where on a cold engine, we descended a six mile grade where the battery filled up halfway down but by the time we reached the bottom, the coolant was at normal full operating temp. However, when I turned off the Rav near the bottom of the grade, the MID showed a trip fuel economy of 99.9 MPG, which if accurate means there was no fuel used that entire time.
Third, even after the battery is full and EV mode becomes disabled, the MID still shows energy going to the battery. I believe this might be true, and I have a suspicion this may not good for the hybrid battery. What I noticed is that during an extended downhill that lasted several miles beyond the point where the hybrid battery became full, I was able to drive on the level ground for more than four miles in EV mode before the ICE kicked in. In another instance, I descended only the bottom part of that hill and hit the same level area with the battery having just gone to eight bars, and was only able to drive for three miles before the ICE came on. Both drives in EV mode were at the same speed and in almost identical conditions.
It is what happens after this supercharging of the battery that is a bit concerning. The next one or two times after a supercharging incident when the Rav is parked for an hour or more, the hybrid battery shows a lower charge state when restarted than it had when it was parked, typically by one but occasionally two bars. After a couple of drive cycles, this behavior goes away. We have an electric car and in instances where the charge state drops when parked, it is primarily due to the battery management system rebalancing the cells because of inconsistent voltage among the individual cells that may indicate an imminent cell failure or from repeated high current charging/discharging. Oue electric car has a Lithium ion battery so it may not be directly comparable to the NiMH in our XLE but this odd behavior isn't confidence inspiring.
We've got a long warranty on our hybrid battery so if it fails within ten years, Toyota will be on the hook for it.
Again, I just want other potential hybrid owners to be aware that very mountainous terrain will exceed the limitations of the hybrid system in ways that limit recovering recovery and generate symptoms which may indicate conditions that might shorten the lifetime of the hybrid battery.
When descending an extended and steep downhill of three or more miles, the hybrid battery will become fully charged and at that time, a few things will happen.
First, the Rav becomes unable to operate in EV mode. The EV mode light turns off, and pressing the EV button generates a message that EV mode is unavailable.
Second, the ICE engine spins up. I'm not sure if there is fuel going to the engine or if it is just being spun up to provide additional drag with fuel flow shut off. When this happens and the engine is not at full operating temperature, the engine coolant gauge will show the engine continues to get warmer. I had one instance where on a cold engine, we descended a six mile grade where the battery filled up halfway down but by the time we reached the bottom, the coolant was at normal full operating temp. However, when I turned off the Rav near the bottom of the grade, the MID showed a trip fuel economy of 99.9 MPG, which if accurate means there was no fuel used that entire time.
Third, even after the battery is full and EV mode becomes disabled, the MID still shows energy going to the battery. I believe this might be true, and I have a suspicion this may not good for the hybrid battery. What I noticed is that during an extended downhill that lasted several miles beyond the point where the hybrid battery became full, I was able to drive on the level ground for more than four miles in EV mode before the ICE kicked in. In another instance, I descended only the bottom part of that hill and hit the same level area with the battery having just gone to eight bars, and was only able to drive for three miles before the ICE came on. Both drives in EV mode were at the same speed and in almost identical conditions.
It is what happens after this supercharging of the battery that is a bit concerning. The next one or two times after a supercharging incident when the Rav is parked for an hour or more, the hybrid battery shows a lower charge state when restarted than it had when it was parked, typically by one but occasionally two bars. After a couple of drive cycles, this behavior goes away. We have an electric car and in instances where the charge state drops when parked, it is primarily due to the battery management system rebalancing the cells because of inconsistent voltage among the individual cells that may indicate an imminent cell failure or from repeated high current charging/discharging. Oue electric car has a Lithium ion battery so it may not be directly comparable to the NiMH in our XLE but this odd behavior isn't confidence inspiring.
We've got a long warranty on our hybrid battery so if it fails within ten years, Toyota will be on the hook for it.
Again, I just want other potential hybrid owners to be aware that very mountainous terrain will exceed the limitations of the hybrid system in ways that limit recovering recovery and generate symptoms which may indicate conditions that might shorten the lifetime of the hybrid battery.
(Dissipated by heat)
