OK. So a school confiscates a phone for a reason and isn't allowed it back for 2 weeks. If the phone is damaged when the school is in possession of it and they break it because of deep discharge of the battery or where it is put. (ours put it in piles of keys where it will get scratched) Could the school be liable for damages?

If I had warranty could I have it replaced? Assuming it wasn't my fault?

Does the school allow such devices to be used during school time ?

Yeah, phones are allowed. Just not when it goes off in the middle of the class. I honestly thought I clicked turned off as I pressed the power button for 10 seconds. Oh well.

It's been confiscated for 2 weeks. (All the other information in my first post)

So could they be liable for damage and have to pay for it?

If phones weren't allowed then no the school is not liable but if they are allowed, then possibly. The school caused the damage through negligence so it is perfectly acceptable for you to claim against them. However the question is: is it really worth it after considering costs etc? If you have a warranty then it would be a much better option to have it fixed/replaced and I would advise you to do this rather than sue the school :)

... they break it because of deep discharge of the battery or where it is put. (ours put it in piles of keys where it will get scratched) ...

If it was destroyed because of the deep-discharge, I would make a warranty claim (or a claim against the school). As I understand what you are saying, the battery was destroyed because not re-charged immediately. Was the possibility of his happening described in your manual?

On the other hand, superficial scratches will not be covered by warranty, although in theory the school could be liable for negligently storing it.

The process of trying to prove liability through neglect is an expensive one, at best a small claims court matter and the amount you receive if you prevail as compensation may be rather small, offset by the fact that you breaking the rules is what set all this in motion. Knowing the rules make you as liable as they are for any damages resulting in your breaking the rules.

You don't even know if ANY damages are done yet, so the value you place on them is moot at this point. Even if it's just a dead battery.

You will find all throughout life that often times another entity is liable for something, but that getting compensation is difficult, expensive, and not worth it.
Add to that the fact that you violated a school rule (excuses don't count for anything in court), your chances have just plummeted.
But feel free to argue your case to the school lawyer. Yes, all schools have one. Might be a good experience. Do it in writing, with step by step facts, and costs to repair, with proof. Keep it to one page.