iPhone 4s drains fully charged battery within 1 hour after it is accidentally plugged into an ipad 3 charger, any fix?

My fully charged iPhone 4s used to last enough for 1 day. Today, I accidentally plugged iPhone into an iPad 3 charger for about 2 hours, then I noticed that it is getting abnormally hot. After this incident, the phone drains battery by decreasing 1% of the battery every minute. I went to see Apple technical support, who tested and said for certain that the problem was the battery (after assuring me that it should be fine to charge iPhone 4s with iPad 3 charger!). After charging me a hefty fee, I left the store, and iphone 4s still drains battery like before. Can my phone be fixed without requiring me to get a new phone? Can I get my money back from Apple techincal support, who gave me a wrong diagosis of my phone?