It's about a year and a half old now (the discharge happened about 6 months after I installed the new battery). You might think the 12V batteries would last longer in hybrids, but that doesn't seem to be the case. Most people's OEM batteries only last 4-5 years. They are smaller capacity batteries since they don't do any cranking.

 

Interestingly, that's something I also heard from the chief mechanic of my local dealer.
He told me that some of their clients managed to get the 12V battery flat just by leaving the radio on for some time, while stuck in some motorway queue.
But after my experience above, I suspect that when the 12V battery doesn't last long it's because it's abused.
I mean, right after I connected the jumper cables and got the car in "READY", I removed the cables and checked the 12V battery voltage: it showed 14V+ already after a few seconds that the car was turned on (and with the petrol engine not yet spinning).
Therefore,obviously the 12V battery was actually being charged by the traction battery bank (through some voltage regulator, I guess).
If this is true (can anyone confirm?) there should be no way to abuse the 12V battery, other than using some 12V equipment without leaving the car on "READY".
In other words, I suspect that whoever flattened the 12V battery with the sound system while stuck in a queue, probably did not leave the car on "READY".
Which is not a good idea, in my opinion.
I understand that if left on "READY", the car will occasionally turn on the V6 to keep the traction batteries from getting too low, but on "READY" there should be no risk to flatten anything, even if using the radio, A/C, headlights, whatever.
And even if the V6 will occasionally turn on when the stay is very long, it's much better than leaving the engine on all the time, as you should do with a non-hybrid car to use the A/C, for instance.
What do you think, have I got it right?

 

I wish I knew positively but your reasoning sounds logical. There are many changes from yours to my 2010 model but I think they're mostly just model change upgrades. The biggest change is the Atkinson combustion system and chain driven valve train. Plus additional horsepower. Oh, and it's the new 'low friction' engine using 0w20w oil.

 

Yes, the 12V battery gets charged from the hybrid battery when the vehicle is in READY mode. There is no alternator to charge the battery as on non-hybrids.

 

Precisely what I thought. Good to know, thanks for confirming.
Actually, I already left the car in READY also for long(ish) stops since I bought it in May, but that was mainly to keep the A/C running in hot summer weather.
Otoh, now I'll stick to that habit also in winter!

 

In the winter, the gas engine will come on more frequently to warm up the engine and to provide heat in the cabin. Part of the heating comes from a small electric heater, but most is still provided by the engine coolant. One some hybrids such as the Prius, grille-blocking techniques can improve gas mileage by retaining heat in the engine bay better, meaning less warm-up time on the engine, but I didn't notice any significant difference after trying it on my RX400h. I only tried blocking the small bumper grille however.

 

Aha, I wasn't aware of that. Where is it located, in the engine compartment or inside?

 

I found some clarification in another discussion here.

 

Interesting stuff, thanks for the link.
I see that they mention the scangauge display, which is something I was also considering.
But I'll make another thread on that, it's O/T on this one...