Iphone 4S battery? Phone fell?

I have an iPhone 4S and i love it. I'll be getting the new one later on this year though. I tossed my iPhone onto my bed and it bounced off onto the carpeted floor. It's in a really sturdy case, i mean this thing has fallen from a 3rd story window onto a sidewalk and nothing happened to it other than a few scratches on the rubber corners ( it's Urban Armour Gear - they're actually awesome cases!).

However, when it bounced onto the carpet, I went to go pick it up and it wouldnt turn on. I tried holding the lock button and home button, etc but nothing worked until I plugged it into the charger. The red 'low battery' thing came up and it started charging and then turned on fine and is working perfectly again now.

But it was at 88% before it was dropped, and when it started up again after being plugged in, it was at 53%. Why did it drop so much?

Mobile phone batteries are just a mystery sometimes and even something as simple as bouncing on the carpet and really mess with the life of the battery. There's really no definite answer here for why it did that. On the upside, your phone still works. I wouldn't worry too much about it unless you have issues later on.