My sister seemed to be obsessed with her iPhone bringing it everywhere with her and I mean even to the table with the greasiest food you could see, watch videos while eating and sadly enough while using the restroom. One day she dropped her phone in the toilet and came to me about it, the phone was able to turn on but it did not keep a charge and eventually after I opened it up and saw the red on the water damage indicators I realized she needed a new battery.
In order to be sure that the problem was the phone's battery I took the phone to a local phone repair shop and plugged in a new battery into the phone and it worked like a miracle. They wanted to charge me $45 for just the battery by itself, another place wanted to install it since they could not sell me the battery just by itself and quoted $77.99 to simply use a new battery it connect it and seal the phone up. So I looked around the web and found iFixit and noticed for about $25 including shipping I got two screwdrivers and the battery and it came in the mail as generally most mail does 3-5 days. I went straight to work and put the battery in the case and pushed the connector down, and managed to put the ant sized screw in the hole and sealed the phone back up.
She got her phone back and I told her to power cycle it and it has been working perfectly since I've got it and the warranty is just a peace of mind.
If you drop your phone in the toilet or get it wet, disregard the bag of rice method, open it up dry it out as much as possible with some type of cloth (Preferably a microfiber), review the damage visibly, and let it sit out in the air for about 48 hours. Afterwards try and charge the phone, if the battery does not charge, it probably needs replacement and try a new one. Worked for me.
Battery installation was very easy about any novice can do it too!