Had an '06 RX400h and never any problem with either the 12V battery or main battery. It was, unfortunately, totalled in a wreck at 145K and still going strong. Never a problem of any kind.
We replaced with a '13 RX450h, and with around 121K, still no problem with either battery on it, either.
Yeah, we are "road runners" :)
Thanks for all the great info, though, I'll be prepared if ever needed!