My iPhone keeps rebooting after water damage.

I have an White iPhone 4 CDMA that fell into a pool for about a minute. That person kept it for a week trying to dry it by taking off the back and drying it with a towel. Then after the week, he gave it to me and I tested it's functionality. It booted when plugged in and the battery as completely dead (it doesn't charge). It said 100% Plugged in on the phone. It dies after like 4-5 minutes of use while plugged in. It's normal functions don't work with dead battery. I tested it with a working battery and it displays the battery percentage right and also dies after 4-5 minutes of use. It works completly fine and then it shuts down. When it shutdowns, the LCD dies out slowly. Like if someone unplugged the battery. Then, I took it completely apart and cleaned the motherboard and other cables thoroughly with isopropyl alcohol. The phone does the same with dead battery. This time it show 2% and does the same. I am going to test it with the working battery later on tomorrow. Is there any way to stop the iPhone from rebooting?

UPDATE:

The battery sorta works. It only chargen to 12%-14% and it does. But it works. It just keeps shutting down by it self.

NOTE:

It has been tested with a new battery and it still shuts down after about 2 minutes of use.