I cannot provide you with the answer just share my experience:
My car is serviced by a Lexus dealer so I told them to order a new battery, then took the car, they fitted and then the bill! Over £200!!! (my previous Ls 400 &430 took a standard 12v battery (cost from Lexus under £100... Explanation provided me : the 12V battery for Ls600 is specially made so as to avoid starting a fire with the hybrid battery. All good and well ... Next time I told the dealer to order me another battery in case the problem I was experiencing was because of the battery. They advised me that the special battery was not immediately available so they would get me a standard battery! (Temporarily? I don't know, in the event I didn't need it.) So I guess it's your choice. Have no idea where you could the special battery other than Toyota/Lexus.