Hi
The 12v battery in my IS 300h has been causing me problems, I've called the AA three times this year.
I've decided to replace it. Went to the local Halfords, they cant help. We to two other dealers. One quoted 'about' £350.00, another said they could get one,but, it would have to be programmed at the factory, price unknown.
Now the good news. I rang Lexus,their technician said, the battery in the boot is a conventional 12v battery (£125.00)
A ctek mxs 5.0, or any trickle charger will be ok. Just connect the clips to the battery first, then switch on and leave.
Hope this helps.