In a couple of weeks I'll be leaving for a long trip, and the car will stay unused for 3 months.
Other than trying to leave it with the batteries on the "green" level, I can't figure what else I could do.
Any ideas? I'd hate to return, find the car stuck and the battery bank to be replaced....
The car is a new to me 2008, and the batteries seem to do their job nicely, as far as I can tell.

 

The smaller 12v is the one you most need to be concerned with. Some folks have said a good trickle charger will keep it up. Lexus say's drive the car at least once a month or if possible have a friend take it to the store for you once a month. Something like that.

 

Really? I would have thought that the builder's suggestion was related to the motors battery bank.
Also because that's obviously the most expensive to replace.
For normal 12V batteries, I already left them unused and uncharged for more than 3 months on other cars, after disconnecting them, and they survived pretty well....

 

Have the oil changed before you store it for 3 months.

 

The hybrid traction battery will be fine. I previously drove a Prius that had sat for 3 years in a wrecking yard, and the hybrid battery was fine (same type of batteries as the 400h). Just keep the 12V battery on a "Battery Tender" or "Noco Genius" charger (something that won't overcharge it), or disconnect the 12V battery, and you'll be fine. Also inflating the tires up to 40-50 would help reduce flat spots.

 

just disconnect the negative terminal on the 12v

 

Why, I never did that on the big block engine of my boat, before storing her for 6 to 8 months...
Any specific reason why the RX 3.3 engine would need that?

 

That's a good point, thanks!

 

This isn't a specific recommendation, I would do this for any vehicle that needs to be stored not just this RX. The reason being, oil has contaminants in it after being run and you don't want them sitting around in your engine for X number of months.

 

Mario, the hybrid is set up differently than most gas only cars. A lot of good suggestions for them would be what was given here by others such as just disconnecting the 12v battery but you don't want to do that in the (h) as it powers so many of the computers that store data including how you drive the car. The best suggestion is to either put a low power device such as the battery tender on it or have a friend drive it once or twice a month for at least 5 miles before shutting it down. If you lose all the data you won't be getting the mileage you're used to until you've driven it quite some time and much of the other stored data will be gone.

Your manual should have a section on that or your local service facility for your (h) can confirm that.

 

Any car with remote entry needs to keep the receiver powered at all times. There are likely one or two other things which which have a continuous very low power draw. The dinky 12v battery in the 400h will eventually be drained to the point it won't "ready" the car. Will that happen in 3 months? Quite probably, unless you've already replaced the 12v with a better one, in which case it's still a gamble. A battery tender or other trickle charger on the 12v will keep the battery from being run down. Disconnecting is ok too, but there are a number of things you need to reset afterwards like the windows.

Oil change before is good, fill the gas tank and add some stabilizer. Personally, instead of pumping up the tires I'd get them off the ground. At least don't inflate past max psi on sidewall.

 

ehhhhh.. unless it's time for an oil change.. i wouldn't change the oil before storage.. i would change it shortly after it's out of storage though.. gas wise, i would leave quarter of a tank and go pump a full tank when out of storage..

but personally, i don't think 3 month isn't THAT long of a time to worry.. i regularly leave my car at the airport for a month at a time.. never a dead battery, even in the winter..

you will probably have a dead battery.. but that's pretty much it.

think about the cars in the dealer lots.. they've been there for a long time.. as long as a year or two without moving.. and they do okay..

 

Thanks everybody, some valuable hints here.
But in the meantime I had a direct experience to report, which might be of interest also for others.

I went with my wife to visit some friends for a week, and since we went around with them, we didn't need our car, so we left it on the road in front of their house.
But as it turned out, my wife forgot the internal light above the rear view mirror turned on (women.... ), so when it was time to drive back home, I pressed the remote and nothing happened.
It didn't took long, after opening the door manually and checking that the dashboard was dead, to find out that the "door/off/on" switch was in the "on" position...

So, what I got was a lesson learned and a completely dead battery, with the blue/white/red eye indicator stuck on white (=recharge).
By the way, even if the car is now 4 years old and the battery is still the original one, I'm 100% sure that the indicator was blue (=OK) just a few days before.

Luckily, it was sufficient to connect some jumper cables to bring the dashboard alive, get the "READY" message, and after a minute hear the V6 spinning.
A few things were lost of course (electric windows, seat memory, GPS settings), but overall the car seemed to work nicely.
On the other hand, when I stopped the car after 10 minutes or so, I had to use the jumper cables again to restart it.
So, even if I knew that the battery couldn't have been recharged so quickly, I was beginning to fear that it was gone forever.

Anyway, considering that we had a 5 hours drive back home, I thought to leave and never stop the car again till our arrival.
After about two hours, I had a look at the battery (always leaving the car on "READY", to avoid the risk of getting stuck again), and the indicator was still white.
Anyhow, the car worked nicely, and brought us at home without missing a beat.
When we arrived and eventually turned off the car, I rechecked the battery indicator, and by this time it was blue again!
In fact, the car now starts just fine, with no need for jumper cables.

So, based on this experience, I don't think it should be a problem to disconnect the battery and/or leave it on a trickle charger when not used for a long time.

Anyway, re. the existing battery, what do you think, should I replace it anyway, considering the deep discharge it went through, or will it still be good?
Oh, well, time will tell, I suppose...

 

Once I had a map light drain my 12V battery in only 2-3 days. I used a battery charger to get it back fully charged and haven't had a problem since. But, my battery was only about a year old at the time. If your battery is 4-5 years old or more, replace it. Costco has good 100-month batteries for about $65.

 

Good to know. And how old is it now?
Since the 12V battery on the hybrid is not stressed at all, I guess it should last a bit longer than other "normal" car batteries....