1 - yes it's 2015. Not sure if you realised but the RX450h has been out for 6 years and a new RX is coming out this year so we aren't talking about a new car here.
2 - the 450h does not suffer from these battery problems. I've left my car for 4 weeks every winter for the last 3 years and it starts fine.
3 - you're plucking figures out of the sky. The 400h wasn't anywhere near the region of £50k, the current RX is and its the most reliable car in its class - period - no ifs no buts, it just is. If there was a major issue, we'd know about it as Lexus sells 100k RXs annually in the US alone