How can I open the trunk when there is no battery in the car?

 

with the key

 

And if you don't have the key, you will need to crawl into the rear hatch area, lift up the rear interior skirt and manually operate the latch.

But the key is a much more elegant solution.

 

Elegant, and easier.

 

I can not turn the key. It would break.

 

Then get crawling...

 

the trunk lock is held in by a clip, and if you pop that and then the lock out, to open the trunk in the future, all you need to do it push down on a little tab

 

There's a good chance you can rescue that trunk lock by soaking it down with penetrating oil, waiting a few hours or days and then gently working it with the key.

And yes, patience is the "key".

 

I've had good luck removing the lock cylinders and soaking them in a jar of automatic trans fluid for a few days. Requires a lot of cleaning once the internals are free but if they're frozen, its a viable option. Every spring I use a graphite on each of my lock cylinders to ensure they stay functioning properly.