2019 Toyota C-HR new car ( 9 months old with 2000 miles) would not start after one week in garage.

I would guess the car is little used and then only for short journeys ? If so , dont waste your money on another battery . You need to charge battery firstly and then run the car every for days 3 / 4 days for 10 or 15 mins .That will be enough to maintain battery .

Thank you for your advice. I go abroad a lot and have never had probs with previous cars when picking them up at home or airport after 4 weeks or so. Why should this one be causing me do much angst.

I heard that you must store the key "at least 30 ft from the vehicle " when it is not in use. The reason is the car is constantly searching/communicating with the key which causes a high current drain on the battery. When the key is out of range, after an hour it will stop searching and go to sleep, with very little drain on the battery. Maybe this applies in your case ?

Thank you. I'll try.