I have an iPhone 6. I left it in my car for a few hours and ever since the battery has been messed up. Will a battery replacement work?

I have an iPhone 6. Back in summer (super hot day, even for summer)I left it in my car for a few hours (by accident) and ever since the battery takes hours to charge and dies within two-threee hours. I found a vendor who will replace the battery, but will it fix my charging and battery life woes? Or could it be something else? My phone is updated to the most recent IOS and I don't really have any apps on it. I don't want to shell out $80 for a new battery if that's not the problem.

A new battery should do the trick. I would order a new one off Amazon and change it myself. There are plenty of YouTube videos to guide you and it's not as hard as you would think. I've changed several screens/batteries on several different models and it saves you some money. Just be sure to read the seller reviews before you buy to make sure you don't receive a bad battery.

Didn't you get some sort of warranty on the phone when you first bought it? Can't you take advantage of that?