Will I mess up my battery in any way if I leave my iPhone 5 dead for a long time?

I was grounded and my mom has my phone and I don't know when ill get it back but its dead and has been for two days. If I leave it dead for too long, will it affect my battery or phone in any way?

Nope won't hurt the battery at all. Just fully recharge it when you are able to.

If the battery completely dies past the 1-2% that it turns its self of at then you can greatly reduce the battery's ability to hold a charge.