Since I was out of the country, my newly purchased 08 Prius stayed in parking lot (very strong sunshine) for 35 days. I did not disconnect the battery. Is that very bad for the car? Is there anything I have to do before I start the engine? Thanks!
If it starts IMHO you don't have to do anything special. The reason I say "if" is because after that long the 12v battery may not have enough juice in it to get things going. Give it a shot and see what happens.
:welcome: Welcome to PriusChat, hans_fh! Your 12V battery may be discharged from a constant small drain on it. If it is discharged, you will have to get a jump-start using another 12V power source. There is a connection under the hood to connect the positive terminal to, and full instructions are in the manual. Be VERY careful not to reverse the polarity of the battery used to provide the jump (+ to - or - to +, connect + to + and - on the charged battery to bare metal on your car). If your car goes to READY, you're ready to go.
I probably would have pulled the dome fuse or, since you parked in the sun, put the 12v on a little solar panel trickle charger before a trip of that length. If you do NOT have SKS or turn it off if you do have it you might get lucky and she'll fire right up for you. If it doesn't start you'll need to get a jump start...remember the jump points are under the hood of the car under the fuse box cover.
It is not bad for the car just the 12 volt battery. As with most newer designed vehicles, the battery has a small drain on them for anti-theft devices and such. My 2003 Corvette can't sit more than 3 weeks without draining the battery dead. So to counter this, I leave a Sears Battery Charger/Maintainer device on the vehicle. Others use a Battery Minder or Battery Tender brand, they do the same thing to keep the battery in great shape, when a vehicle is not driven daily or stored.
